Python's Walrus Operator

The Walrus operator := goal is to allow a user to name variables and use them in expressions with ease. It takes the form of NAME := expr. Below is an example:

while data := file.read(1024):
    process(data)

In this example, each time the while loop is run, data will be set to the output of file.read(1024) until there is no data left to read. Each loop will run the process function on each 1024 chunk of data. While this is a super simple example, it shows that you can assign the output of an expression file.read(1024) to a variable in the while expression.

This Operator also allows a user to reuse an expression in the case of regex matching.

import re
pattern = re.compile("foo")
if (match := pattern.search("This is just foobar")) is not None:
    print(match.group())

We are saving one line of code by using the walrus operator, as you can see here. Since an alternative way of writing this is:

import re
pattern = re.compile("foo")
match   = pattern.search("This is just foobar")
if match is not None:
    print(match.group())

Obviously, in real-world examples, you would be doing more than just printing.

Links: https://www.python.org/dev/peps/pep-0572/