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What is an assignment expression?
An assignment expression, also known as the “walrus operator” because of its resemblance to the eyes and tusks of a walrus, is a feature in some programming languages that allows you to assign a value to a variable as part of an expression. It was introduced in Python 3.8 as the := operator.
The role and usage of assignment expressions
The primary role of assignment expressions is to improve code readability and reduce duplication by eliminating the need for intermediate variables. They can be particularly useful in conditional expressions and while loops.
One common use case of assignment expressions is in conditional statements. Previously, you would have needed to assign a value to a variable before using it in an if statement. With assignment expressions, you can now write more compact and readable code:
“`
# Without assignment expression
value = get_value()
if value > 10:
result = “Large”
else:
result = “Small”
# With assignment expression
if (value := get_value()) > 10:
result = “Large”
else:
result = “Small”
“`
In the above example, the assignment expression `(value := get_value())` assigns the value returned by the `get_value()` function to the variable `value` while evaluating the condition. This eliminates the need for a separate line of code to assign the value.
Assignment expressions can also be used in while loops to assign values and evaluate conditions:
“`
# Without assignment expression
line = input()
while line != “quit”:
process(line)
line = input()
# With assignment expression
while (line := input()) != “quit”:
process(line)
“`
In this example, the assignment expression `(line := input())` assigns the user input to the variable `line` while evaluating the condition of the while loop.
Assignment expressions are a powerful tool that can simplify code and make it more expressive. However, it’s important to use them judiciously and ensure they enhance readability rather than hinder it.
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