a += b
a -= b
a *= b
a /= b
a %= b
a &= b
a |= b
a ^= b
a <<= b
a >>= b
++a
--a
a++
a--
+a
-a
a + b
a - b
a * b
a / b
a % b
~a
a & b
a | b
a ^ b
a << b
a >> b
!a
a && b
a || b
a == b
a != b
a < b
a > b
a <= b
a >= b
a[b]
*a
&a
a->b
a.b
a(...)
a, b
(type) a
a ? b : c
sizeof
_Alignof
(since C11)
for Assignment operators |
What is an assignment operator in c.
Assignment Operators in C are used to assign values to the variables. They come under the category of binary operators as they require two operands to operate upon. The left side operand is called a variable and the right side operand is the value. The value on the right side of the "=" is assigned to the variable on the left side of "=". The value on the right side must be of the same data type as the variable on the left side. Hence, the associativity is from right to left.
In this C tutorial , we'll understand the types of C programming assignment operators with examples. To delve deeper you can enroll in our C Programming Course .
Before going in-depth about assignment operators you must know about operators in C. If you haven't visited the Operators in C tutorial, refer to Operators in C: Types of Operators .
There are two types of assignment operators in C:
+= | addition assignment | It adds the right operand to the left operand and assigns the result to the left operand. |
-= | subtraction assignment | It subtracts the right operand from the left operand and assigns the result to the left operand. |
*= | multiplication assignment | It multiplies the right operand with the left operand and assigns the result to the left operand |
/= | division assignment | It divides the left operand with the right operand and assigns the result to the left operand. |
%= | modulo assignment | It takes modulus using two operands and assigns the result to the left operand. |
There can be five combinations of bitwise operators with the assignment operator, "=". Let's look at them one by one.
&= | bitwise AND assignment | It performs the bitwise AND operation on the variable with the value on the right |
|= | bitwise OR assignment | It performs the bitwise OR operation on the variable with the value on the right |
^= | bitwise XOR assignment | It performs the bitwise XOR operation on the variable with the value on the right |
<<= | bitwise left shift assignment | Shifts the bits of the variable to the left by the value on the right |
>>= | bitwise right shift assignment | Shifts the bits of the variable to the right by the value on the right |
Practice problems on assignment operators in c, 1. what will the value of "x" be after the execution of the following code.
The correct answer is 52. x starts at 50, increases by 5 to 55, then decreases by 3 to 52.
The correct answer is 144. After right-shifting 73 (binary 1001001) by one and then left-shifting the result by two, the value becomes 144 (binary 10010000).
While performing arithmetic operations with the same variable, use compound assignment operators
When mixing assignments with other operations, use parentheses to ensure the correct order of evaluation.
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The assignment ( = ) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.
A valid assignment target, including an identifier or a property accessor . It can also be a destructuring assignment pattern .
An expression specifying the value to be assigned to x .
The value of y .
Thrown in strict mode if assigning to an identifier that is not declared in the scope.
Thrown in strict mode if assigning to a property that is not modifiable .
The assignment operator is completely different from the equals ( = ) sign used as syntactic separators in other locations, which include:
All these places accept an assignment expression on the right-hand side of the = , so if you have multiple equals signs chained together:
This is equivalent to:
Which means y must be a pre-existing variable, and x is a newly declared const variable. y is assigned the value 5 , and x is initialized with the value of the y = 5 expression, which is also 5 . If y is not a pre-existing variable, a global variable y is implicitly created in non-strict mode , or a ReferenceError is thrown in strict mode. To declare two variables within the same declaration, use:
Value of assignment expressions.
The assignment expression itself evaluates to the value of the right-hand side, so you can log the value and assign to a variable at the same time.
The global object sits at the top of the scope chain. When attempting to resolve a name to a value, the scope chain is searched. This means that properties on the global object are conveniently visible from every scope, without having to qualify the names with globalThis. or window. or global. .
Because the global object has a String property ( Object.hasOwn(globalThis, "String") ), you can use the following code:
So the global object will ultimately be searched for unqualified identifiers. You don't have to type globalThis.String ; you can just type the unqualified String . To make this feature more conceptually consistent, assignment to unqualified identifiers will assume you want to create a property with that name on the global object (with globalThis. omitted), if there is no variable of the same name declared in the scope chain.
In strict mode , assignment to an unqualified identifier in strict mode will result in a ReferenceError , to avoid the accidental creation of properties on the global object.
Note that the implication of the above is that, contrary to popular misinformation, JavaScript does not have implicit or undeclared variables. It just conflates the global object with the global scope and allows omitting the global object qualifier during property creation.
The left-hand side of can also be an assignment pattern. This allows assigning to multiple variables at once.
For more information, see Destructuring assignment .
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Table of Contents
The assignment operator, assignments and variables, other assignment syntax, initializing and updating variables, making multiple variables refer to the same object, updating lists through indices and slices, adding and updating dictionary keys, doing parallel assignments, unpacking iterables, providing default argument values, augmented mathematical assignment operators, augmented assignments for concatenation and repetition, augmented bitwise assignment operators, annotated assignment statements, assignment expressions with the walrus operator, managed attribute assignments, define or call a function, work with classes, import modules and objects, use a decorator, access the control variable in a for loop or a comprehension, use the as keyword, access the _ special variable in an interactive session, built-in objects, named constants.
Python’s assignment operators allow you to define assignment statements . This type of statement lets you create, initialize, and update variables throughout your code. Variables are a fundamental cornerstone in every piece of code, and assignment statements give you complete control over variable creation and mutation.
Learning about the Python assignment operator and its use for writing assignment statements will arm you with powerful tools for writing better and more robust Python code.
In this tutorial, you’ll:
You’ll dive deep into Python’s assignment statements. To get the most out of this tutorial, you should be comfortable with several basic topics, including variables , built-in data types , comprehensions , functions , and Python keywords . Before diving into some of the later sections, you should also be familiar with intermediate topics, such as object-oriented programming , constants , imports , type hints , properties , descriptors , and decorators .
Free Source Code: Click here to download the free assignment operator source code that you’ll use to write assignment statements that allow you to create, initialize, and update variables in your code.
One of the most powerful programming language features is the ability to create, access, and mutate variables . In Python, a variable is a name that refers to a concrete value or object, allowing you to reuse that value or object throughout your code.
To create a new variable or to update the value of an existing one in Python, you’ll use an assignment statement . This statement has the following three components:
Here’s how an assignment statement will generally look in Python:
Here, variable represents a generic Python variable, while expression represents any Python object that you can provide as a concrete value—also known as a literal —or an expression that evaluates to a value.
To execute an assignment statement like the above, Python runs the following steps:
The second step shows that variables work differently in Python than in other programming languages. In Python, variables aren’t containers for objects. Python variables point to a value or object through its memory address. They store memory addresses rather than objects.
This behavior difference directly impacts how data moves around in Python, which is always by reference . In most cases, this difference is irrelevant in your day-to-day coding, but it’s still good to know.
The central component of an assignment statement is the assignment operator . This operator is represented by the = symbol, which separates two operands:
Operators are special symbols that perform mathematical , logical , and bitwise operations in a programming language. The objects (or object) on which an operator operates are called operands .
Unary operators, like the not Boolean operator, operate on a single object or operand, while binary operators act on two. That means the assignment operator is a binary operator.
Note: Like C , Python uses == for equality comparisons and = for assignments. Unlike C, Python doesn’t allow you to accidentally use the assignment operator ( = ) in an equality comparison.
Equality is a symmetrical relationship, and assignment is not. For example, the expression a == 42 is equivalent to 42 == a . In contrast, the statement a = 42 is correct and legal, while 42 = a isn’t allowed. You’ll learn more about illegal assignments later on.
The right-hand operand in an assignment statement can be any Python object, such as a number , list , string , dictionary , or even a user-defined object. It can also be an expression. In the end, expressions always evaluate to concrete objects, which is their return value.
Here are a few examples of assignments in Python:
The first two sample assignments in this code snippet use concrete values, also known as literals , to create and initialize number and greeting . The third example assigns the result of a math expression to the total variable, while the last example uses a Boolean expression.
Note: You can use the built-in id() function to inspect the memory address stored in a given variable.
Here’s a short example of how this function works:
The number in your output represents the memory address stored in number . Through this address, Python can access the content of number , which is the integer 42 in this example.
If you run this code on your computer, then you’ll get a different memory address because this value varies from execution to execution and computer to computer.
Unlike expressions, assignment statements don’t have a return value because their purpose is to make the association between the variable and its value. That’s why the Python interpreter doesn’t issue any output in the above examples.
Now that you know the basics of how to write an assignment statement, it’s time to tackle why you would want to use one.
The assignment statement is the explicit way for you to associate a name with an object in Python. You can use this statement for two main purposes:
When you use a variable name as the left operand in an assignment statement for the first time, you’re creating a new variable. At the same time, you’re initializing the variable to point to the value of the right operand.
On the other hand, when you use an existing variable in a new assignment, you’re updating or mutating the variable’s value. Strictly speaking, every new assignment will make the variable refer to a new value and stop referring to the old one. Python will garbage-collect all the values that are no longer referenced by any existing variable.
Assignment statements not only assign a value to a variable but also determine the data type of the variable at hand. This additional behavior is another important detail to consider in this kind of statement.
Because Python is a dynamically typed language, successive assignments to a given variable can change the variable’s data type. Changing the data type of a variable during a program’s execution is considered bad practice and highly discouraged. It can lead to subtle bugs that can be difficult to track down.
Unlike in math equations, in Python assignments, the left operand must be a variable rather than an expression or a value. For example, the following construct is illegal, and Python flags it as invalid syntax:
In this example, you have expressions on both sides of the = sign, and this isn’t allowed in Python code. The error message suggests that you may be confusing the equality operator with the assignment one, but that’s not the case. You’re really running an invalid assignment.
To correct this construct and convert it into a valid assignment, you’ll have to do something like the following:
In this code snippet, you first import the sqrt() function from the math module. Then you isolate the hypotenuse variable in the original equation by using the sqrt() function. Now your code works correctly.
Now you know what kind of syntax is invalid. But don’t get the idea that assignment statements are rigid and inflexible. In fact, they offer lots of room for customization, as you’ll learn next.
Python’s assignment statements are pretty flexible and versatile. You can write them in several ways, depending on your specific needs and preferences. Here’s a quick summary of the main ways to write assignments in Python:
Up to this point, you’ve mostly learned about the base assignment syntax in the above code snippet. In the following sections, you’ll learn about multiple, parallel, and augmented assignments. You’ll also learn about assignments with iterable unpacking.
Read on to see the assignment statements in action!
You’ll find and use assignment statements everywhere in your Python code. They’re a fundamental part of the language, providing an explicit way to create, initialize, and mutate variables.
You can use assignment statements with plain names, like number or counter . You can also use assignments in more complicated scenarios, such as with:
This list isn’t exhaustive. However, it gives you some idea of how flexible these statements are. You can even assign multiple values to an equal number of variables in a single line, commonly known as parallel assignment . Additionally, you can simultaneously assign the values in an iterable to a comma-separated group of variables in what’s known as an iterable unpacking operation.
In the following sections, you’ll dive deeper into all these topics and a few other exciting things that you can do with assignment statements in Python.
The most elementary use case of an assignment statement is to create a new variable and initialize it using a particular value or expression:
All these statements create new variables, assigning them initial values or expressions. For an initial value, you should always use the most sensible and least surprising value that you can think of. For example, initializing a counter to something different from 0 may be confusing and unexpected because counters almost always start having counted no objects.
Updating a variable’s current value or state is another common use case of assignment statements. In Python, assigning a new value to an existing variable doesn’t modify the variable’s current value. Instead, it causes the variable to refer to a different value. The previous value will be garbage-collected if no other variable refers to it.
Consider the following examples:
These examples run two consecutive assignments on the same variable. The first one assigns the string "Hello, World!" to a new variable named greeting .
The second assignment updates the value of greeting by reassigning it the "Hi, Pythonistas!" string. In this example, the original value of greeting —the "Hello, World!" string— is lost and garbage-collected. From this point on, you can’t access the old "Hello, World!" string.
Even though running multiple assignments on the same variable during a program’s execution is common practice, you should use this feature with caution. Changing the value of a variable can make your code difficult to read, understand, and debug. To comprehend the code fully, you’ll have to remember all the places where the variable was changed and the sequential order of those changes.
Because assignments also define the data type of their target variables, it’s also possible for your code to accidentally change the type of a given variable at runtime. A change like this can lead to breaking errors, like AttributeError exceptions. Remember that strings don’t have the same methods and attributes as lists or dictionaries, for example.
In Python, you can make several variables reference the same object in a multiple-assignment line. This can be useful when you want to initialize several similar variables using the same initial value:
In this example, you chain two assignment operators in a single line. This way, your two variables refer to the same initial value of 0 . Note how both variables hold the same memory address, so they point to the same instance of 0 .
When it comes to integer variables, Python exhibits a curious behavior. It provides a numeric interval where multiple assignments behave the same as independent assignments. Consider the following examples:
To create n and m , you use independent assignments. Therefore, they should point to different instances of the number 42 . However, both variables hold the same object, which you confirm by comparing their corresponding memory addresses.
Now check what happens when you use a greater initial value:
Now n and m hold different memory addresses, which means they point to different instances of the integer number 300 . In contrast, when you use multiple assignments, both variables refer to the same object. This tiny difference can save you small bits of memory if you frequently initialize integer variables in your code.
The implicit behavior of making independent assignments point to the same integer number is actually an optimization called interning . It consists of globally caching the most commonly used integer values in day-to-day programming.
Under the hood, Python defines a numeric interval in which interning takes place. That’s the interning interval for integer numbers. You can determine this interval using a small script like the following:
This script helps you determine the interning interval by comparing integer numbers from -10 to 500 . If you run the script from your command line, then you’ll get an output like the following:
This output means that if you use a single number between -5 and 256 to initialize several variables in independent statements, then all these variables will point to the same object, which will help you save small bits of memory in your code.
In contrast, if you use a number that falls outside of the interning interval, then your variables will point to different objects instead. Each of these objects will occupy a different memory spot.
You can use the assignment operator to mutate the value stored at a given index in a Python list. The operator also works with list slices . The syntax to write these types of assignment statements is the following:
In the first construct, expression can return any Python object, including another list. In the second construct, expression must return a series of values as a list, tuple, or any other sequence. You’ll get a TypeError if expression returns a single value.
Note: When creating slice objects, you can use up to three arguments. These arguments are start , stop , and step . They define the number that starts the slice, the number at which the slicing must stop retrieving values, and the step between values.
Here’s an example of updating an individual value in a list:
In this example, you update the value at index 2 using an assignment statement. The original number at that index was 7 , and after the assignment, the number is 3 .
Note: Using indices and the assignment operator to update a value in a tuple or a character in a string isn’t possible because tuples and strings are immutable data types in Python.
Their immutability means that you can’t change their items in place :
You can’t use the assignment operator to change individual items in tuples or strings. These data types are immutable and don’t support item assignments.
It’s important to note that you can’t add new values to a list by using indices that don’t exist in the target list:
In this example, you try to add a new value to the end of numbers by using an index that doesn’t exist. This assignment isn’t allowed because there’s no way to guarantee that new indices will be consecutive. If you ever want to add a single value to the end of a list, then use the .append() method.
If you want to update several consecutive values in a list, then you can use slicing and an assignment statement:
In the first example, you update the letters between indices 1 and 3 without including the letter at 3 . The second example updates the letters from index 3 until the end of the list. Note that this slicing appends a new value to the list because the target slice is shorter than the assigned values.
Also note that the new values were provided through a tuple, which means that this type of assignment allows you to use other types of sequences to update your target list.
The third example updates a single value using a slice where both indices are equal. In this example, the assignment inserts a new item into your target list.
In the final example, you use a step of 2 to replace alternating letters with their lowercase counterparts. This slicing starts at index 1 and runs through the whole list, stepping by two items each time.
Updating the value of an existing key or adding new key-value pairs to a dictionary is another common use case of assignment statements. To do these operations, you can use the following syntax:
The first construct helps you update the current value of an existing key, while the second construct allows you to add a new key-value pair to the dictionary.
For example, to update an existing key, you can do something like this:
In this example, you update the current inventory of oranges in your store using an assignment. The left operand is the existing dictionary key, and the right operand is the desired new value.
While you can’t add new values to a list by assignment, dictionaries do allow you to add new key-value pairs using the assignment operator. In the example below, you add a lemon key to inventory :
In this example, you successfully add a new key-value pair to your inventory with 100 units. This addition is possible because dictionaries don’t have consecutive indices but unique keys, which are safe to add by assignment.
The assignment statement does more than assign the result of a single expression to a single variable. It can also cope nicely with assigning multiple values to multiple variables simultaneously in what’s known as a parallel assignment .
Here’s the general syntax for parallel assignments in Python:
Note that the left side of the statement can be either a tuple or a list of variables. Remember that to create a tuple, you just need a series of comma-separated elements. In this case, these elements must be variables.
The right side of the statement must be a sequence or iterable of values or expressions. In any case, the number of elements in the right operand must match the number of variables on the left. Otherwise, you’ll get a ValueError exception.
In the following example, you compute the two solutions of a quadratic equation using a parallel assignment:
In this example, you first import sqrt() from the math module. Then you initialize the equation’s coefficients in a parallel assignment.
The equation’s solution is computed in another parallel assignment. The left operand contains a tuple of two variables, x1 and x2 . The right operand consists of a tuple of expressions that compute the solutions for the equation. Note how each result is assigned to each variable by position.
A classical use case of parallel assignment is to swap values between variables:
The highlighted line does the magic and swaps the values of previous_value and next_value at the same time. Note that in a programming language that doesn’t support this kind of assignment, you’d have to use a temporary variable to produce the same effect:
In this example, instead of using parallel assignment to swap values between variables, you use a new variable to temporarily store the value of previous_value to avoid losing its reference.
For a concrete example of when you’d need to swap values between variables, say you’re learning how to implement the bubble sort algorithm , and you come up with the following function:
In the highlighted line, you use a parallel assignment to swap values in place if the current value is less than the next value in the input list. To dive deeper into the bubble sort algorithm and into sorting algorithms in general, check out Sorting Algorithms in Python .
You can use assignment statements for iterable unpacking in Python. Unpacking an iterable means assigning its values to a series of variables one by one. The iterable must be the right operand in the assignment, while the variables must be the left operand.
Like in parallel assignments, the variables must come as a tuple or list. The number of variables must match the number of values in the iterable. Alternatively, you can use the unpacking operator ( * ) to grab several values in a variable if the number of variables doesn’t match the iterable length.
Here’s the general syntax for iterable unpacking in Python:
Iterable unpacking is a powerful feature that you can use all around your code. It can help you write more readable and concise code. For example, you may find yourself doing something like this:
Whenever you do something like this in your code, go ahead and replace it with a more readable iterable unpacking using a single and elegant assignment, like in the following code snippet:
The numbers list on the right side contains four values. The assignment operator unpacks these values into the four variables on the left side of the statement. The values in numbers get assigned to variables in the same order that they appear in the iterable. The assignment is done by position.
Note: Because Python sets are also iterables, you can use them in an iterable unpacking operation. However, it won’t be clear which value goes to which variable because sets are unordered data structures.
The above example shows the most common form of iterable unpacking in Python. The main condition for the example to work is that the number of variables matches the number of values in the iterable.
What if you don’t know the iterable length upfront? Will the unpacking work? It’ll work if you use the * operator to pack several values into one of your target variables.
For example, say that you want to unpack the first and second values in numbers into two different variables. Additionally, you would like to pack the rest of the values in a single variable conveniently called rest . In this case, you can use the unpacking operator like in the following code:
In this example, first and second hold the first and second values in numbers , respectively. These values are assigned by position. The * operator packs all the remaining values in the input iterable into rest .
The unpacking operator ( * ) can appear at any position in your series of target variables. However, you can only use one instance of the operator:
The iterable unpacking operator works in any position in your list of variables. Note that you can only use one unpacking operator per assignment. Using more than one unpacking operator isn’t allowed and raises a SyntaxError .
Dropping away unwanted values from the iterable is a common use case for the iterable unpacking operator. Consider the following example:
In Python, if you want to signal that a variable won’t be used, then you use an underscore ( _ ) as the variable’s name. In this example, useful holds the only value that you need to use from the input iterable. The _ variable is a placeholder that guarantees that the unpacking works correctly. You won’t use the values that end up in this disposable variable.
Note: In the example above, if your target iterable is a sequence data type, such as a list or tuple, then it’s best to access its last item directly.
To do this, you can use the -1 index:
Using -1 gives you access to the last item of any sequence data type. In contrast, if you’re dealing with iterators , then you won’t be able to use indices. That’s when the *_ syntax comes to your rescue.
The pattern used in the above example comes in handy when you have a function that returns multiple values, and you only need a few of these values in your code. The os.walk() function may provide a good example of this situation.
This function allows you to iterate over the content of a directory recursively. The function returns a generator object that yields three-item tuples. Each tuple contains the following items:
Now say that you want to iterate over your home directory and list only the files. You can do something like this:
This code will issue a long output depending on the current content of your home directory. Note that you need to provide a string with the path to your user folder for the example to work. The _ placeholder variable will hold the unwanted data.
In contrast, the filenames variable will hold the list of files in the current directory, which is the data that you need. The code will print the list of filenames. Go ahead and give it a try!
The assignment operator also comes in handy when you need to provide default argument values in your functions and methods. Default argument values allow you to define functions that take arguments with sensible defaults. These defaults allow you to call the function with specific values or to simply rely on the defaults.
As an example, consider the following function:
This function takes one argument, called name . This argument has a sensible default value that’ll be used when you call the function without arguments. To provide this sensible default value, you use an assignment.
Note: According to PEP 8 , the style guide for Python code, you shouldn’t use spaces around the assignment operator when providing default argument values in function definitions.
Here’s how the function works:
If you don’t provide a name during the call to greet() , then the function uses the default value provided in the definition. If you provide a name, then the function uses it instead of the default one.
Up to this point, you’ve learned a lot about the Python assignment operator and how to use it for writing different types of assignment statements. In the following sections, you’ll dive into a great feature of assignment statements in Python. You’ll learn about augmented assignments .
Python supports what are known as augmented assignments . An augmented assignment combines the assignment operator with another operator to make the statement more concise. Most Python math and bitwise operators have an augmented assignment variation that looks something like this:
Note that $ isn’t a valid Python operator. In this example, it’s a placeholder for a generic operator. This statement works as follows:
In practice, an augmented assignment like the above is equivalent to the following statement:
As you can conclude, augmented assignments are syntactic sugar . They provide a shorthand notation for a specific and popular kind of assignment.
For example, say that you need to define a counter variable to count some stuff in your code. You can use the += operator to increment counter by 1 using the following code:
In this example, the += operator, known as augmented addition , adds 1 to the previous value in counter each time you run the statement counter += 1 .
It’s important to note that unlike regular assignments, augmented assignments don’t create new variables. They only allow you to update existing variables. If you use an augmented assignment with an undefined variable, then you get a NameError :
Python evaluates the right side of the statement before assigning the resulting value back to the target variable. In this specific example, when Python tries to compute x + 1 , it finds that x isn’t defined.
Great! You now know that an augmented assignment consists of combining the assignment operator with another operator, like a math or bitwise operator. To continue this discussion, you’ll learn which math operators have an augmented variation in Python.
An equation like x = x + b doesn’t make sense in math. But in programming, a statement like x = x + b is perfectly valid and can be extremely useful. It adds b to x and reassigns the result back to x .
As you already learned, Python provides an operator to shorten x = x + b . Yes, the += operator allows you to write x += b instead. Python also offers augmented assignment operators for most math operators. Here’s a summary:
Operator | Description | Example | Equivalent |
---|---|---|---|
Adds the right operand to the left operand and stores the result in the left operand | |||
Subtracts the right operand from the left operand and stores the result in the left operand | |||
Multiplies the right operand with the left operand and stores the result in the left operand | |||
Divides the left operand by the right operand and stores the result in the left operand | |||
Performs of the left operand by the right operand and stores the result in the left operand | |||
Finds the remainder of dividing the left operand by the right operand and stores the result in the left operand | |||
Raises the left operand to the power of the right operand and stores the result in the left operand |
The Example column provides generic examples of how to use the operators in actual code. Note that x must be previously defined for the operators to work correctly. On the other hand, y can be either a concrete value or an expression that returns a value.
Note: The matrix multiplication operator ( @ ) doesn’t support augmented assignments yet.
Consider the following example of matrix multiplication using NumPy arrays:
Note that the exception traceback indicates that the operation isn’t supported yet.
To illustrate how augmented assignment operators work, say that you need to create a function that takes an iterable of numeric values and returns their sum. You can write this function like in the code below:
In this function, you first initialize total to 0 . In each iteration, the loop adds a new number to total using the augmented addition operator ( += ). When the loop terminates, total holds the sum of all the input numbers. Variables like total are known as accumulators . The += operator is typically used to update accumulators.
Note: Computing the sum of a series of numeric values is a common operation in programming. Python provides the built-in sum() function for this specific computation.
Another interesting example of using an augmented assignment is when you need to implement a countdown while loop to reverse an iterable. In this case, you can use the -= operator:
In this example, custom_reversed() is a generator function because it uses yield . Calling the function creates an iterator that yields items from the input iterable in reverse order. To decrement the control variable, index , you use an augmented subtraction statement that subtracts 1 from the variable in every iteration.
Note: Similar to summing the values in an iterable, reversing an iterable is also a common requirement. Python provides the built-in reversed() function for this specific computation, so you don’t have to implement your own. The above example only intends to show the -= operator in action.
Finally, counters are a special type of accumulators that allow you to count objects. Here’s an example of a letter counter:
To create this counter, you use a Python dictionary. The keys store the letters. The values store the counts. Again, to increment the counter, you use an augmented addition.
Counters are so common in programming that Python provides a tool specially designed to facilitate the task of counting. Check out Python’s Counter: The Pythonic Way to Count Objects for a complete guide on how to use this tool.
The += and *= augmented assignment operators also work with sequences , such as lists, tuples, and strings. The += operator performs augmented concatenations , while the *= operator performs augmented repetition .
These operators behave differently with mutable and immutable data types:
Operator | Description | Example |
---|---|---|
Runs an augmented concatenation operation on the target sequence. Mutable sequences are updated in place. If the sequence is immutable, then a new sequence is created and assigned back to the target name. | ||
Adds to itself times. Mutable sequences are updated in place. If the sequence is immutable, then a new sequence is created and assigned back to the target name. |
Note that the augmented concatenation operator operates on two sequences, while the augmented repetition operator works on a sequence and an integer number.
Consider the following examples and pay attention to the result of calling the id() function:
Mutable sequences like lists support the += augmented assignment operator through the .__iadd__() method, which performs an in-place addition. This method mutates the underlying list, appending new values to its end.
Note: If the left operand is mutable, then x += y may not be completely equivalent to x = x + y . For example, if you do list_1 = list_1 + list_2 instead of list_1 += list_2 above, then you’ll create a new list instead of mutating the existing one. This may be important if other variables refer to the same list.
Immutable sequences, such as tuples and strings, don’t provide an .__iadd__() method. Therefore, augmented concatenations fall back to the .__add__() method, which doesn’t modify the sequence in place but returns a new sequence.
There’s another difference between mutable and immutable sequences when you use them in an augmented concatenation. Consider the following examples:
With mutable sequences, the data to be concatenated can come as a list, tuple, string, or any other iterable. In contrast, with immutable sequences, the data can only come as objects of the same type. You can concatenate tuples to tuples and strings to strings, for example.
Again, the augmented repetition operator works with a sequence on the left side of the operator and an integer on the right side. This integer value represents the number of repetitions to get in the resulting sequence:
When the *= operator operates on a mutable sequence, it falls back to the .__imul__() method, which performs the operation in place, modifying the underlying sequence. In contrast, if *= operates on an immutable sequence, then .__mul__() is called, returning a new sequence of the same type.
Note: Values of n less than 0 are treated as 0 , which returns an empty sequence of the same data type as the target sequence on the left side of the *= operand.
Note that a_list[0] is a_list[3] returns True . This is because the *= operator doesn’t make a copy of the repeated data. It only reflects the data. This behavior can be a source of issues when you use the operator with mutable values.
For example, say that you want to create a list of lists to represent a matrix, and you need to initialize the list with n empty lists, like in the following code:
In this example, you use the *= operator to populate matrix with three empty lists. Now check out what happens when you try to populate the first sublist in matrix :
The appended values are reflected in the three sublists. This happens because the *= operator doesn’t make copies of the data that you want to repeat. It only reflects the data. Therefore, every sublist in matrix points to the same object and memory address.
If you ever need to initialize a list with a bunch of empty sublists, then use a list comprehension :
This time, when you populate the first sublist of matrix , your changes aren’t propagated to the other sublists. This is because all the sublists are different objects that live in different memory addresses.
Bitwise operators also have their augmented versions. The logic behind them is similar to that of the math operators. The following table summarizes the augmented bitwise operators that Python provides:
Operator | Operation | Example | Equivalent |
---|---|---|---|
Augmented bitwise AND ( ) | |||
Augmented bitwise OR ( ) | |||
Augmented bitwise XOR ( ) | |||
Augmented bitwise right shift | |||
Augmented bitwise left shift |
The augmented bitwise assignment operators perform the intended operation by taking the current value of the left operand as a starting point for the computation. Consider the following example, which uses the & and &= operators:
Programmers who work with high-level languages like Python rarely use bitwise operations in day-to-day coding. However, these types of operations can be useful in some situations.
For example, say that you’re implementing a Unix-style permission system for your users to access a given resource. In this case, you can use the characters "r" for reading, "w" for writing, and "x" for execution permissions, respectively. However, using bit-based permissions could be more memory efficient:
You can assign permissions to your users with the OR bitwise operator or the augmented OR bitwise operator. Finally, you can use the bitwise AND operator to check if a user has a certain permission, as you did in the final two examples.
You’ve learned a lot about augmented assignment operators and statements in this and the previous sections. These operators apply to math, concatenation, repetition, and bitwise operations. Now you’re ready to look at other assignment variants that you can use in your code or find in other developers’ code.
So far, you’ve learned that Python’s assignment statements and the assignment operator are present in many different scenarios and use cases. Those use cases include variable creation and initialization, parallel assignments, iterable unpacking, augmented assignments, and more.
In the following sections, you’ll learn about a few variants of assignment statements that can be useful in your future coding. You can also find these assignment variants in other developers’ code. So, you should be aware of them and know how they work in practice.
In short, you’ll learn about:
These topics will take you through several interesting and useful examples that showcase the power of Python’s assignment statements.
PEP 526 introduced a dedicated syntax for variable annotation back in Python 3.6 . The syntax consists of the variable name followed by a colon ( : ) and the variable type:
Even though these statements declare three variables with their corresponding data types, the variables aren’t actually created or initialized. So, for example, you can’t use any of these variables in an augmented assignment statement:
If you try to use one of the previously declared variables in an augmented assignment, then you get a NameError because the annotation syntax doesn’t define the variable. To actually define it, you need to use an assignment.
The good news is that you can use the variable annotation syntax in an assignment statement with the = operator:
The first statement in this example is what you can call an annotated assignment statement in Python. You may ask yourself why you should use type annotations in this type of assignment if everybody can see that counter holds an integer number. You’re right. In this example, the variable type is unambiguous.
However, imagine what would happen if you found a variable initialization like the following:
What would be the data type of each user in users ? If the initialization of users is far away from the definition of the User class, then there’s no quick way to answer this question. To clarify this ambiguity, you can provide the appropriate type hint for users :
Now you’re clearly communicating that users will hold a list of User instances. Using type hints in assignment statements that initialize variables to empty collection data types—such as lists, tuples, or dictionaries—allows you to provide more context about how your code works. This practice will make your code more explicit and less error-prone.
Up to this point, you’ve learned that regular assignment statements with the = operator don’t have a return value. They just create or update variables. Therefore, you can’t use a regular assignment to assign a value to a variable within the context of an expression.
Python 3.8 changed this by introducing a new type of assignment statement through PEP 572 . This new statement is known as an assignment expression or named expression .
Note: Expressions are a special type of statement in Python. Their distinguishing characteristic is that expressions always have a return value, which isn’t the case with all types of statements.
Unlike regular assignments, assignment expressions have a return value, which is why they’re called expressions in the first place. This return value is automatically assigned to a variable. To write an assignment expression, you must use the walrus operator ( := ), which was named for its resemblance to the eyes and tusks of a walrus lying on its side.
The general syntax of an assignment statement is as follows:
This expression looks like a regular assignment. However, instead of using the assignment operator ( = ), it uses the walrus operator ( := ). For the expression to work correctly, the enclosing parentheses are required in most use cases. However, there are certain situations in which these parentheses are superfluous. Either way, they won’t hurt you.
Assignment expressions come in handy when you want to reuse the result of an expression or part of an expression without using a dedicated assignment to grab this value beforehand.
Note: Assignment expressions with the walrus operator have several practical use cases. They also have a few restrictions. For example, they’re illegal in certain contexts, such as lambda functions, parallel assignments, and augmented assignments.
For a deep dive into this special type of assignment, check out The Walrus Operator: Python 3.8 Assignment Expressions .
A particularly handy use case for assignment expressions is when you need to grab the result of an expression used in the context of a conditional statement. For example, say that you need to write a function to compute the mean of a sample of numeric values. Without the walrus operator, you could do something like this:
In this example, the sample size ( n ) is a value that you need to reuse in two different computations. First, you need to check whether the sample has data points or not. Then you need to use the sample size to compute the mean. To be able to reuse n , you wrote a dedicated assignment statement at the beginning of your function to grab the sample size.
You can avoid this extra step by combining it with the first use of the target value, len(sample) , using an assignment expression like the following:
The assignment expression introduced in the conditional computes the sample size and assigns it to n . This way, you guarantee that you have a reference to the sample size to use in further computations.
Because the assignment expression returns the sample size anyway, the conditional can check whether that size equals 0 or not and then take a certain course of action depending on the result of this check. The return statement computes the sample’s mean and sends the result back to the function caller.
Python provides a few tools that allow you to fine-tune the operations behind the assignment of attributes. The attributes that run implicit operations on assignments are commonly referred to as managed attributes .
Properties are the most commonly used tool for providing managed attributes in your classes. However, you can also use descriptors and, in some cases, the .__setitem__() special method.
To understand what fine-tuning the operation behind an assignment means, say that you need a Point class that only allows numeric values for its coordinates, x and y . To write this class, you must set up a validation mechanism to reject non-numeric values. You can use properties to attach the validation functionality on top of x and y .
Here’s how you can write your class:
In Point , you use properties for the .x and .y coordinates. Each property has a getter and a setter method . The getter method returns the attribute at hand. The setter method runs the input validation using a try … except block and the built-in float() function. Then the method assigns the result to the actual attribute.
Here’s how your class works in practice:
When you use a property-based attribute as the left operand in an assignment statement, Python automatically calls the property’s setter method, running any computation from it.
Because both .x and .y are properties, the input validation runs whenever you assign a value to either attribute. In the first example, the input values are valid numbers and the validation passes. In the final example, "one" isn’t a valid numeric value, so the validation fails.
If you look at your Point class, you’ll note that it follows a repetitive pattern, with the getter and setter methods looking quite similar. To avoid this repetition, you can use a descriptor instead of a property.
A descriptor is a class that implements the descriptor protocol , which consists of four special methods :
Here’s how your code may look if you use a descriptor to represent the coordinates of your Point class:
You’ve removed repetitive code by defining Coordinate as a descriptor that manages the input validation in a single place. Go ahead and run the following code to try out the new implementation of Point :
Great! The class works as expected. Thanks to the Coordinate descriptor, you now have a more concise and non-repetitive version of your original code.
Another way to fine-tune the operations behind an assignment statement is to provide a custom implementation of .__setitem__() in your class. You’ll use this method in classes representing mutable data collections, such as custom list-like or dictionary-like classes.
As an example, say that you need to create a dictionary-like class that stores its keys in lowercase letters:
In this example, you create a dictionary-like class by subclassing UserDict from collections . Your class implements a .__setitem__() method, which takes key and value as arguments. The method uses str.lower() to convert key into lowercase letters before storing it in the underlying dictionary.
Python implicitly calls .__setitem__() every time you use a key as the left operand in an assignment statement. This behavior allows you to tweak how you process the assignment of keys in your custom dictionary.
Python implicitly runs assignments in many different contexts. In most cases, these implicit assignments are part of the language syntax. In other cases, they support specific behaviors.
Whenever you complete an action in the following list, Python runs an implicit assignment for you:
Behind the scenes, Python performs an assignment in every one of the above situations. In the following subsections, you’ll take a tour of all these situations.
When you define a function, the def keyword implicitly assigns a function object to your function’s name. Here’s an example:
From this point on, the name greet refers to a function object that lives at a given memory address in your computer. You can call the function using its name and a pair of parentheses with appropriate arguments. This way, you can reuse greet() wherever you need it.
If you call your greet() function with fellow as an argument, then Python implicitly assigns the input argument value to the name parameter on the function’s definition. The parameter will hold a reference to the input arguments.
When you define a class with the class keyword, you’re assigning a specific name to a class object . You can later use this name to create instances of that class. Consider the following example:
In this example, the name User holds a reference to a class object, which was defined in __main__.User . Like with a function, when you call the class’s constructor with the appropriate arguments to create an instance, Python assigns the arguments to the parameters defined in the class initializer .
Another example of implicit assignments is the current instance of a class, which in Python is called self by convention. This name implicitly gets a reference to the current object whenever you instantiate a class. Thanks to this implicit assignment, you can access .name and .job from within the class without getting a NameError in your code.
Import statements are another variant of implicit assignments in Python. Through an import statement, you assign a name to a module object, class, function, or any other imported object. This name is then created in your current namespace so that you can access it later in your code:
In this example, you import the sys module object from the standard library and assign it to the sys name, which is now available in your namespace, as you can conclude from the second call to the built-in dir() function.
You also run an implicit assignment when you use a decorator in your code. The decorator syntax is just a shortcut for a formal assignment like the following:
Here, you call decorator() with a function object as an argument. This call will typically add functionality on top of the existing function, func() , and return a function object, which is then reassigned to the func name.
The decorator syntax is syntactic sugar for replacing the previous assignment, which you can now write as follows:
Even though this new code looks pretty different from the above assignment, the code implicitly runs the same steps.
Another situation in which Python automatically runs an implicit assignment is when you use a for loop or a comprehension. In both cases, you can have one or more control variables that you then use in the loop or comprehension body:
The memory address of control_variable changes on each iteration of the loop. This is because Python internally reassigns a new value from the loop iterable to the loop control variable on each cycle.
The same behavior appears in comprehensions:
In the end, comprehensions work like for loops but use a more concise syntax. This comprehension creates a new list of strings that mimic the output from the previous example.
The as keyword in with statements, except clauses, and import statements is another example of an implicit assignment in Python. This time, the assignment isn’t completely implicit because the as keyword provides an explicit way to define the target variable.
In a with statement, the target variable that follows the as keyword will hold a reference to the context manager that you’re working with. As an example, say that you have a hello.txt file with the following content:
You want to open this file and print each of its lines on your screen. In this case, you can use the with statement to open the file using the built-in open() function.
In the example below, you accomplish this. You also add some calls to print() that display information about the target variable defined by the as keyword:
This with statement uses the open() function to open hello.txt . The open() function is a context manager that returns a text file object represented by an io.TextIOWrapper instance.
Since you’ve defined a hello target variable with the as keyword, now that variable holds a reference to the file object itself. You confirm this by printing the object and its memory address. Finally, the for loop iterates over the lines and prints this content to the screen.
When it comes to using the as keyword in the context of an except clause, the target variable will contain an exception object if any exception occurs:
In this example, you run a division that raises a ZeroDivisionError . The as keyword assigns the raised exception to error . Note that when you print the exception object, you get only the message because exceptions have a custom .__str__() method that supports this behavior.
There’s a final detail to remember when using the as specifier in a try … except block like the one in the above example. Once you leave the except block, the target variable goes out of scope , and you can’t use it anymore.
Finally, Python’s import statements also support the as keyword. In this context, you can use as to import objects with a different name:
In these examples, you use the as keyword to import the numpy package with the np name and pandas with the name pd . If you call dir() , then you’ll realize that np and pd are now in your namespace. However, the numpy and pandas names are not.
Using the as keyword in your imports comes in handy when you want to use shorter names for your objects or when you need to use different objects that originally had the same name in your code. It’s also useful when you want to make your imported names non-public using a leading underscore, like in import sys as _sys .
The final implicit assignment that you’ll learn about in this tutorial only occurs when you’re using Python in an interactive session. Every time you run a statement that returns a value, the interpreter stores the result in a special variable denoted by a single underscore character ( _ ).
You can access this special variable as you’d access any other variable:
These examples cover several situations in which Python internally uses the _ variable. The first two examples evaluate expressions. Expressions always have a return value, which is automatically assigned to the _ variable every time.
When it comes to function calls, note that if your function returns a fruitful value, then _ will hold it. In contrast, if your function returns None , then the _ variable will remain untouched.
The next example consists of a regular assignment statement. As you already know, regular assignments don’t return any value, so the _ variable isn’t updated after these statements run. Finally, note that accessing a variable in an interactive session returns the value stored in the target variable. This value is then assigned to the _ variable.
Note that since _ is a regular variable, you can use it in other expressions:
In this example, you first create a list of values. Then you call len() to get the number of values in the list. Python automatically stores this value in the _ variable. Finally, you use _ to compute the mean of your list of values.
Now that you’ve learned about some of the implicit assignments that Python runs under the hood, it’s time to dig into a final assignment-related topic. In the following few sections, you’ll learn about some illegal and dangerous assignments that you should be aware of and avoid in your code.
In Python, you’ll find a few situations in which using assignments is either forbidden or dangerous. You must be aware of these special situations and try to avoid them in your code.
In the following sections, you’ll learn when using assignment statements isn’t allowed in Python. You’ll also learn about some situations in which using assignments should be avoided if you want to keep your code consistent and robust.
You can’t use Python keywords as variable names in assignment statements. This kind of assignment is explicitly forbidden. If you try to use a keyword as a variable name in an assignment, then you get a SyntaxError :
Whenever you try to use a keyword as the left operand in an assignment statement, you get a SyntaxError . Keywords are an intrinsic part of the language and can’t be overridden.
If you ever feel the need to name one of your variables using a Python keyword, then you can append an underscore to the name of your variable:
In this example, you’re using the desired name for your variables. Because you added a final underscore to the names, Python doesn’t recognize them as keywords, so it doesn’t raise an error.
Note: Even though adding an underscore at the end of a name is an officially recommended practice , it can be confusing sometimes. Therefore, try to find an alternative name or use a synonym whenever you find yourself using this convention.
For example, you can write something like this:
In this example, using the name booking_class for your variable is way clearer and more descriptive than using class_ .
You’ll also find that you can use only a few keywords as part of the right operand in an assignment statement. Those keywords will generally define simple statements that return a value or object. These include lambda , and , or , not , True , False , None , in , and is . You can also use the for keyword when it’s part of a comprehension and the if keyword when it’s used as part of a ternary operator .
In an assignment, you can never use a compound statement as the right operand. Compound statements are those that require an indented block, such as for and while loops, conditionals, with statements, try … except blocks, and class or function definitions.
Sometimes, you need to name variables, but the desired or ideal name is already taken and used as a built-in name. If this is your case, think harder and find another name. Don’t shadow the built-in.
Shadowing built-in names can cause hard-to-identify problems in your code. A common example of this issue is using list or dict to name user-defined variables. In this case, you override the corresponding built-in names, which won’t work as expected if you use them later in your code.
Consider the following example:
The exception in this example may sound surprising. How come you can’t use list() to build a list from a call to map() that returns a generator of square numbers?
By using the name list to identify your list of numbers, you shadowed the built-in list name. Now that name points to a list object rather than the built-in class. List objects aren’t callable, so your code no longer works.
In Python, you’ll have nothing that warns against using built-in, standard-library, or even relevant third-party names to identify your own variables. Therefore, you should keep an eye out for this practice. It can be a source of hard-to-debug errors.
In programming, a constant refers to a name associated with a value that never changes during a program’s execution. Unlike other programming languages, Python doesn’t have a dedicated syntax for defining constants. This fact implies that Python doesn’t have constants in the strict sense of the word.
Python only has variables. If you need a constant in Python, then you’ll have to define a variable and guarantee that it won’t change during your code’s execution. To do that, you must avoid using that variable as the left operand in an assignment statement.
To tell other Python programmers that a given variable should be treated as a constant, you must write your variable’s name in capital letters with underscores separating the words. This naming convention has been adopted by the Python community and is a recommendation that you’ll find in the Constants section of PEP 8 .
In the following examples, you define some constants in Python:
The problem with these constants is that they’re actually variables. Nothing prevents you from changing their value during your code’s execution. So, at any time, you can do something like the following:
These assignments modify the value of two of your original constants. Python doesn’t complain about these changes, which can cause issues later in your code. As a Python developer, you must guarantee that named constants in your code remain constant.
The only way to do that is never to use named constants in an assignment statement other than the constant definition.
You’ve learned a lot about Python’s assignment operators and how to use them for writing assignment statements . With this type of statement, you can create, initialize, and update variables according to your needs. Now you have the required skills to fully manage the creation and mutation of variables in your Python code.
In this tutorial, you’ve learned how to:
Learning about the Python assignment operator and how to use it in assignment statements is a fundamental skill in Python. It empowers you to write reliable and effective Python code.
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Python's Assignment Operator: Write Robust Assignments (Source Code)
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There are different kinds of the operators, such as arithmetic, relational, bitwise, assignment, etc., in the C programming language. The assignment operator is used to assign the value, variable and function to another variable. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=.
It is the operator used to assign the right side operand or variable to the left side variable.
Let's create a program to use the simple assignment operator in C.
The operator is used to add the left side operand to the left operand and then assign results to the left operand.
Let's create a program to use the Plus and assign operator in C.
The operator is used to subtract the left operand with the right operand and then assigns the result to the left operand.
Let's create a program to use the Subtract and Assign (-=) operator in C.
The operator is used to multiply the left operand with the right operand and then assign result to the left operand.
Let's create a program to use the multiply and assign operator (*=) in C.
An operator is used between the left and right operands, which divides the first number by the second number to return the result in the left operand.
Let's create a program to use the divide and assign operator (/=) in C.
An operator used between the left operand and the right operand divides the first number (n1) by the second number (n2) and returns the remainder in the left operand.
Let's create a program to use the divide and assign operator (%=) in C.
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C# examples, c# assignment operators, assignment operators.
Assignment operators are used to assign values to variables.
In the example below, we use the assignment operator ( = ) to assign the value 10 to a variable called x :
Try it Yourself »
The addition assignment operator ( += ) adds a value to a variable:
A list of all assignment operators:
Operator | Example | Same As | Try it |
---|---|---|---|
= | x = 5 | x = 5 | |
+= | x += 3 | x = x + 3 | |
-= | x -= 3 | x = x - 3 | |
*= | x *= 3 | x = x * 3 | |
/= | x /= 3 | x = x / 3 | |
%= | x %= 3 | x = x % 3 | |
&= | x &= 3 | x = x & 3 | |
|= | x |= 3 | x = x | 3 | |
^= | x ^= 3 | x = x ^ 3 | |
>>= | x >>= 3 | x = x >> 3 | |
<<= | x <<= 3 | x = x << 3 |
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What are the differences between the assignment operators = and <- in R?
I know that operators are slightly different, as this example shows
But is this the only difference?
The difference in assignment operators is clearer when you use them to set an argument value in a function call. For example:
In this case, x is declared within the scope of the function, so it does not exist in the user workspace.
In this case, x is declared in the user workspace, so you can use it after the function call has been completed.
There is a general preference among the R community for using <- for assignment (other than in function signatures) for compatibility with (very) old versions of S-Plus. Note that the spaces help to clarify situations like
Most R IDEs have keyboard shortcuts to make <- easier to type. Ctrl + = in Architect, Alt + - in RStudio ( Option + - under macOS), Shift + - (underscore) in emacs+ESS.
If you prefer writing = to <- but want to use the more common assignment symbol for publicly released code (on CRAN, for example), then you can use one of the tidy_* functions in the formatR package to automatically replace = with <- .
The answer to the question "Why does x <- y = 5 throw an error but not x <- y <- 5 ?" is "It's down to the magic contained in the parser". R's syntax contains many ambiguous cases that have to be resolved one way or another. The parser chooses to resolve the bits of the expression in different orders depending on whether = or <- was used.
To understand what is happening, you need to know that assignment silently returns the value that was assigned. You can see that more clearly by explicitly printing, for example print(x <- 2 + 3) .
Secondly, it's clearer if we use prefix notation for assignment. So
The parser interprets x <- y <- 5 as
We might expect that x <- y = 5 would then be
but actually it gets interpreted as
This is because = is lower precedence than <- , as shown on the ?Syntax help page.
As your example shows, = and <- have slightly different operator precedence (which determines the order of evaluation when they are mixed in the same expression). In fact, ?Syntax in R gives the following operator precedence table, from highest to lowest:
… ‘-> ->>’ rightwards assignment ‘<- <<-’ assignment (right to left) ‘=’ assignment (right to left) …
Since you were asking about the assignment operators : yes, that is the only difference. However, you would be forgiven for believing otherwise. Even the R documentation of ?assignOps claims that there are more differences:
The operator <- can be used anywhere, whereas the operator = is only allowed at the top level (e.g., in the complete expression typed at the command prompt) or as one of the subexpressions in a braced list of expressions.
Let’s not put too fine a point on it: the R documentation is wrong . This is easy to show: we just need to find a counter-example of the = operator that isn’t (a) at the top level, nor (b) a subexpression in a braced list of expressions (i.e. {…; …} ). — Without further ado:
Clearly we’ve performed an assignment, using = , outside of contexts (a) and (b). So, why has the documentation of a core R language feature been wrong for decades?
It’s because in R’s syntax the symbol = has two distinct meanings that get routinely conflated (even by experts, including in the documentation cited above):
So how does R decide whether a given usage of = refers to the operator or to named argument passing? Let’s see.
In any piece of code of the general form …
… the = is the token that defines named argument passing: it is not the assignment operator. Furthermore, = is entirely forbidden in some syntactic contexts:
Any of these will raise an error “unexpected '=' in ‹bla›”.
In any other context, = refers to the assignment operator call. In particular, merely putting parentheses around the subexpression makes any of the above (a) valid, and (b) an assignment . For instance, the following performs assignment:
Now you might object that such code is atrocious (and you may be right). But I took this code from the base::file.copy function (replacing <- with = ) — it’s a pervasive pattern in much of the core R codebase.
The original explanation by John Chambers , which the the R documentation is probably based on, actually explains this correctly:
[ = assignment is] allowed in only two places in the grammar: at the top level (as a complete program or user-typed expression); and when isolated from surrounding logical structure, by braces or an extra pair of parentheses.
In sum, by default the operators <- and = do the same thing. But either of them can be overridden separately to change its behaviour. By contrast, <- and -> (left-to-right assignment), though syntactically distinct, always call the same function. Overriding one also overrides the other. Knowing this is rarely practical but it can be used for some fun shenanigans .
Google's R style guide simplifies the issue by prohibiting the "=" for assignment. Not a bad choice.
https://google.github.io/styleguide/Rguide.xml
The R manual goes into nice detail on all 5 assignment operators.
http://stat.ethz.ch/R-manual/R-patched/library/base/html/assignOps.html
x = y = 5 is equivalent to x = (y = 5) , because the assignment operators "group" right to left, which works. Meaning: assign 5 to y , leaving the number 5; and then assign that 5 to x .
This is not the same as (x = y) = 5 , which doesn't work! Meaning: assign the value of y to x , leaving the value of y ; and then assign 5 to, umm..., what exactly?
When you mix the different kinds of assignment operators, <- binds tighter than = . So x = y <- 5 is interpreted as x = (y <- 5) , which is the case that makes sense.
Unfortunately, x <- y = 5 is interpreted as (x <- y) = 5 , which is the case that doesn't work!
See ?Syntax and ?assignOps for the precedence (binding) and grouping rules.
According to John Chambers, the operator = is only allowed at "the top level," which means it is not allowed in control structures like if , making the following programming error illegal.
As he writes, "Disallowing the new assignment form [=] in control expressions avoids programming errors (such as the example above) that are more likely with the equal operator than with other S assignments."
You can manage to do this if it's "isolated from surrounding logical structure, by braces or an extra pair of parentheses," so if ((x = 0)) 1 else x would work.
See http://developer.r-project.org/equalAssign.html
From the official R documentation :
The operators <- and = assign into the environment in which they are evaluated. The operator <- can be used anywhere, whereas the operator = is only allowed at the top level (e.g., in the complete expression typed at the command prompt) or as one of the subexpressions in a braced list of expressions.
This may also add to understanding of the difference between those two operators:
For the first element R has assigned values and proper name, while the name of the second element looks a bit strange.
R version 3.3.2 (2016-10-31); macOS Sierra 10.12.1
I am not sure if Patrick Burns book R inferno has been cited here where in 8.2.26 = is not a synonym of <- Patrick states "You clearly do not want to use '<-' when you want to set an argument of a function.". The book is available at https://www.burns-stat.com/documents/books/the-r-inferno/
There are some differences between <- and = in the past version of R or even the predecessor language of R (S language). But currently, it seems using = only like any other modern language (python, java) won't cause any problem. You can achieve some more functionality by using <- when passing a value to some augments while also creating a global variable at the same time but it may have weird/unwanted behavior like in
Highly recommended! Try to read this article which is the best article that tries to explain the difference between those two: Check https://colinfay.me/r-assignment/
Also, think about <- as a function that invisibly returns a value.
See: https://adv-r.hadley.nz/functions.html
Assignment operators in python.
The Python Operators are used to perform operations on values and variables. These are the special symbols that carry out arithmetic, logical, and bitwise computations. The value the operator operates on is known as the Operand. Here, we will cover Different Assignment operators in Python .
Operators |
| ||
---|---|---|---|
| = | Assign the value of the right side of the expression to the left side operand | c = a + b |
| += | Add right side operand with left side operand and then assign the result to left operand | a += b |
| -= | Subtract right side operand from left side operand and then assign the result to left operand | a -= b |
| *= | Multiply right operand with left operand and then assign the result to the left operand | a *= b |
| /= | Divide left operand with right operand and then assign the result to the left operand | a /= b |
| %= | Divides the left operand with the right operand and then assign the remainder to the left operand | a %= b |
| //= | Divide left operand with right operand and then assign the value(floor) to left operand | a //= b |
| **= | Calculate exponent(raise power) value using operands and then assign the result to left operand | a **= b |
| &= | Performs Bitwise AND on operands and assign the result to left operand | a &= b |
| |= | Performs Bitwise OR on operands and assign the value to left operand | a |= b |
| ^= | Performs Bitwise XOR on operands and assign the value to left operand | a ^= b |
| >>= | Performs Bitwise right shift on operands and assign the result to left operand | a >>= b |
| <<= | Performs Bitwise left shift on operands and assign the result to left operand | a <<= b |
| := | Assign a value to a variable within an expression | a := exp |
Here are the Assignment Operators in Python with examples.
Assignment Operators are used to assign values to variables. This operator is used to assign the value of the right side of the expression to the left side operand.
The Addition Assignment Operator is used to add the right-hand side operand with the left-hand side operand and then assigning the result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the addition assignment operator which will first perform the addition operation and then assign the result to the variable on the left-hand side.
The Subtraction Assignment Operator is used to subtract the right-hand side operand from the left-hand side operand and then assigning the result to the left-hand side operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the subtraction assignment operator which will first perform the subtraction operation and then assign the result to the variable on the left-hand side.
The Multiplication Assignment Operator is used to multiply the right-hand side operand with the left-hand side operand and then assigning the result to the left-hand side operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the multiplication assignment operator which will first perform the multiplication operation and then assign the result to the variable on the left-hand side.
The Division Assignment Operator is used to divide the left-hand side operand with the right-hand side operand and then assigning the result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the division assignment operator which will first perform the division operation and then assign the result to the variable on the left-hand side.
The Modulus Assignment Operator is used to take the modulus, that is, it first divides the operands and then takes the remainder and assigns it to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the modulus assignment operator which will first perform the modulus operation and then assign the result to the variable on the left-hand side.
The Floor Division Assignment Operator is used to divide the left operand with the right operand and then assigs the result(floor value) to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the floor division assignment operator which will first perform the floor division operation and then assign the result to the variable on the left-hand side.
The Exponentiation Assignment Operator is used to calculate the exponent(raise power) value using operands and then assigning the result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the exponentiation assignment operator which will first perform exponent operation and then assign the result to the variable on the left-hand side.
The Bitwise AND Assignment Operator is used to perform Bitwise AND operation on both operands and then assigning the result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the bitwise AND assignment operator which will first perform Bitwise AND operation and then assign the result to the variable on the left-hand side.
The Bitwise OR Assignment Operator is used to perform Bitwise OR operation on the operands and then assigning result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the bitwise OR assignment operator which will first perform bitwise OR operation and then assign the result to the variable on the left-hand side.
The Bitwise XOR Assignment Operator is used to perform Bitwise XOR operation on the operands and then assigning result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the bitwise XOR assignment operator which will first perform bitwise XOR operation and then assign the result to the variable on the left-hand side.
The Bitwise Right Shift Assignment Operator is used to perform Bitwise Right Shift Operation on the operands and then assign result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the bitwise right shift assignment operator which will first perform bitwise right shift operation and then assign the result to the variable on the left-hand side.
The Bitwise Left Shift Assignment Operator is used to perform Bitwise Left Shift Opertator on the operands and then assign result to the left operand.
Example: In this code we have two variables ‘a’ and ‘b’ and assigned them with some integer value. Then we have used the bitwise left shift assignment operator which will first perform bitwise left shift operation and then assign the result to the variable on the left-hand side.
The Walrus Operator in Python is a new assignment operator which is introduced in Python version 3.8 and higher. This operator is used to assign a value to a variable within an expression.
Example: In this code, we have a Python list of integers. We have used Python Walrus assignment operator within the Python while loop . The operator will solve the expression on the right-hand side and assign the value to the left-hand side operand ‘x’ and then execute the remaining code.
Similar reads.
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The following are the assignment operators defined in Visual Basic.
^= Operator
*= Operator
/= Operator
\= Operator
+= Operator
-= Operator
<<= Operator
>>= Operator
&= Operator
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Learn how to efficiently handle null values in C# using the null-coalescing operator. This guide covers the syntax, practical applications, and advanced techniques to enhance your programming skills.
Handling null values efficiently is a common requirement in software development. C# offers powerful tools to manage nulls, including the null-coalescing operator (??). This article explores the null-coalescing operator, its benefits, and how it can simplify and enhance your code.
Combining with null-conditional operator, chaining null-coalescing operators, the null-coalescing assignment operator, practical examples.
The null-coalescing operator (??) in C# allows you to provide a default value for an expression that might be null. This operator simplifies the handling of null values, making your code more readable and less error-prone.
The syntax of the null-coalescing operator is straightforward.
In this example, displayName is assigned the value "Guest" because the name is null.
The null-conditional operator (?.) can be used with the null-coalescing operator to safely navigate through potential null references.
In this example, a person.Address?.The city evaluates to null, so "Unknown" is returned.
You can chain multiple null-coalescing operators to provide multiple fallback values.
In this example, firstNonNullName is assigned the first non-null value in the chain, which is "John".
Introduced in C# 8.0, the null-coalescing assignment operator (??=) assigns a value to a variable if it is currently null.
Here, the name is assigned "Default Name" because it was initially null.
Example 1. Default Configuration.
Example 2. Safe Navigation with Fallback
Traditional approach.
Before these operators were available, handling null values required explicit null checks, which could be verbose and cumbersome.
With the null-coalescing operator and null-conditional operator, the same logic becomes much simpler and more readable.
The null-coalescing operator (??) and its companion, the null-coalescing assignment operator (??=), provide powerful and concise ways to handle null values in C#. They significantly reduce the boilerplate code needed for null checks and make your code more readable and maintainable. By mastering these operators, you can write cleaner, more robust C# code that efficiently handles null values.
Object Oriented Programming Using C#
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Assignment operators are used in programming to assign values to variables. We use an assignment operator to store and update data within a program. They enable programmers to store data in variables and manipulate that data. The most common assignment operator is the equals sign (=), which assigns the value on the right side of the operator to ...
Assignment Operator: An assignment operator is the operator used to assign a new value to a variable, property, event or indexer element in C# programming language. Assignment operators can also be used for logical operations such as bitwise logical operations or operations on integral operands and Boolean operands. Unlike in C++, assignment ...
In this article. The assignment operator = assigns the value of its right-hand operand to a variable, a property, or an indexer element given by its left-hand operand. The result of an assignment expression is the value assigned to the left-hand operand. The type of the right-hand operand must be the same as the type of the left-hand operand or implicitly convertible to it.
Different types of assignment operators are shown below: 1. "=": This is the simplest assignment operator. This operator is used to assign the value on the right to the variable on the left. Example: a = 10; b = 20; ch = 'y'; 2. "+=": This operator is combination of '+' and '=' operators. This operator first adds the current ...
for assignments to class type objects, the right operand could be an initializer list only when the assignment is defined by a user-defined assignment operator. removed user-defined assignment constraint. CWG 1538. C++11. E1 ={E2} was equivalent to E1 = T(E2) ( T is the type of E1 ), this introduced a C-style cast. it is equivalent to E1 = T{E2}
The built-in assignment operators return the value of the object specified by the left operand after the assignment (and the arithmetic/logical operation in the case of compound assignment operators). The resultant type is the type of the left operand. The result of an assignment expression is always an l-value.
What is a Certificate? ... Assignment Operators. Assignment operators are used to assign values to variables. In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x: Example. int x = 10;
Simple assignment operator. Assigns values from right side operands to left side operand. C = A + B will assign the value of A + B to C. +=. Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand. C += A is equivalent to C = C + A. -=.
Discussion. The assignment operator allows us to change the value of a modifiable data object (for beginning programmers this typically means a variable). It is associated with the concept of moving a value into the storage location (again usually a variable). Within C++ programming language the symbol used is the equal symbol.
The assignment operators in C can both transform and assign values in a single operation. C provides the following assignment operators: | =. In assignment, the type of the right-hand value is converted to the type of the left-hand value, and the value is stored in the left operand after the assignment has taken place.
In C++, the addition assignment operator (+=) combines the addition operation with the variable assignment allowing you to increment the value of variable by a specified expression in a concise and efficient way. Syntax. variable += value; This above expression is equivalent to the expression: variable = variable + value; Example.
Assignment performs implicit conversion from the value of rhs to the type of lhs and then replaces the value in the object designated by lhs with the converted value of rhs . Assignment also returns the same value as what was stored in lhs (so that expressions such as a = b = c are possible). The value category of the assignment operator is non ...
Assignment Operators in C are used to assign values to the variables. They come under the category of binary operators as they require two operands to operate upon. The left side operand is called a variable and the right side operand is the value. The value on the right side of the "=" is assigned to the variable on the left side of "=".
Assignment (=) The assignment ( =) operator is used to assign a value to a variable or property. The assignment expression itself has a value, which is the assigned value. This allows multiple assignments to be chained in order to assign a single value to multiple variables.
The central component of an assignment statement is the assignment operator. This operator is represented by the = symbol, which separates two operands: A variable ; A value or an expression that evaluates to a concrete value; Operators are special symbols that perform mathematical, logical, and bitwise operations in a programming language.
Assignment Operator. The assignment operator allows us to change the value of a modifiable data object (for beginning programmers this typically means a variable). It is associated with the concept of moving a value into the storage location (again usually a variable). Within C++ programming language the symbol used is the equal symbol.
An assignment operator is used to replace the data of a previously initialized object with some other object's data. A& operator=(const A& rhs) {data_ = rhs.data_; return *this;} For example: A aa; A a; a = aa; // assignment operator You could replace copy construction by default construction plus assignment, but that would be less efficient.
The assignment operator is used to assign the value, variable and function to another variable. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. Example of the Assignment Operators: A = 5; // use Assignment symbol to assign 5 to the operand A. B = A; // Assign operand A to the B.
variable operator value; Types of Assignment Operators in Java. The Assignment Operator is generally of two types. They are: 1. Simple Assignment Operator: The Simple Assignment Operator is used with the "=" sign where the left side consists of the operand and the right side consists of a value. The value of the right side must be of the same data type that has been defined on the left side.
What is a Certificate? ... Assignment Operators. Assignment operators are used to assign values to variables. In the example below, we use the assignment operator (=) to assign the value 10 to a variable called x: Example int x = 10;
The operators <- and = assign into the environment in which they are evaluated. The operator <- can be used anywhere, whereas the operator = is only allowed at the top level (e.g., in the complete expression typed at the command prompt) or as one of the subexpressions in a braced list of expressions.
An assignment operator is an operator that is used to assign some value to a variable. Like normally in Python, we write "a = 5" to assign value 5 to variable 'a'. Augmented assignment operators have a special role to play in Python programming. It basically combines the functioning of the arithmetic or bitwise operator with the assignment operator
The following are the assignment operators defined in Visual Basic. = Operator ^= Operator *= Operator /= Operator \= Operator += Operator-= Operator <<= Operator >>= Operator &= Operator. See also. Operator Precedence in Visual Basic; Operators Listed by Functionality; Statements
This article explores the null-coalescing operator, its benefits, and how it can simplify and enhance your code. Table of Contents. Introduction to Null-Coalescing Operator; Basic Usage of Null-Coalescing Operator; Combining with Null-Conditional Operator; Chaining Null-Coalescing Operators; The Null-Coalescing Assignment Operator; Practical ...