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The Walrus operator
The walrus operator (:=) is perhaps the most controversial operator in the history of Python. Guido was so unhappy with the proposal that he even stepped down permanently from his BDFL role after he accepted this operator as part of PEP 572.
As the name suggests, the walrus operator inherits its name from the two eyes and the teeth represented by the colon (
:) and the equal (
=) operators in conjunction. It is a higher order form of assignment expression designed to do two things at once,
Lets consider an example,
When you match a pattern for a regular expression, you save the result in a variable
res which may or may not be
None. You have to check for NoneTypes before retreiving the groups from the matched pattern.
>>> res = re.match(r'\s') >>> if res: ... print(res.group(0))
With the introduction of the walrus operator, you can now write the same code as,
>>> if(res := re.match(r'\s')): ... print(res.group(0))
The operator is used as part of an expression, so writing
y:=f(x) is invalid. It has to be surrounded by parenthesis like,
(y:=f(x)). This might be a bit wierd because generally Python doesnt enforce the usage of parenthesis as part of its design language. Beyond this caveat, there are few other criticisms with the introduction of this operator,
Hate it or like it, the walrus operator is officially part of Python 3.8!