Walrus Operator in Python

The walrus operator is a new feature introduced in Python 3.8 that allows you to assign a value to a variable as part of an expression. This can be useful in situations where you want to reduce the number of lines of code and make your code more concise. In this lesson, we'll explore how to use the walrus operator in Python and some examples of where it can be useful.

Using the Walrus Operator

The walrus operator is denoted by := and is used to assign a value to a variable as part of an expression. The variable can then be used later in the same expression. Here's an example of how to use the walrus operator to check if a file exists and read its contents in a single line of code:

import os

if (file_path := "myfile.txt") and os.path.exists(file_path):
    with open(file_path) as f:
        contents = f.read()
        print(contents)

In this example, the walrus operator is used to assign the file path to the variable file_path and check if it exists using the os.path.exists function. If the file exists, its contents are read and printed to the console.

Examples of Using the Walrus Operator

Here are some examples of how you can use the walrus operator to make your code more concise:

• Assigning the result of a function to a variable only if the function returns a non-None value

if (result := my_function()) is not None:
    print(result)

• Iterating over a list and using the current value only if it meets a certain condition

my_list = [1, 2, 3, 4, 5]
while (value := my_list.pop()) > 3:
    print(value)

• Checking if a key exists in a dictionary and using its value if it does

my_dict = {"key": "value"}
if (value := my_dict.get("key")) is not None:
    print(value)

Conclusion

The walrus operator is a new feature in Python 3.8 that allows you to assign a value to a variable as part of an expression. This can be useful in situations where you want to reduce the number of lines of code and make your code more concise. The walrus operator is denoted by := and can be used in a variety of ways to make your code more readable and maintainable.