Assignment Expressions

E256161

Python language feature expression construct

Assignment Expressions are a Python language feature introduced by PEP 572 that allow assigning values to variables as part of larger expressions using the “walrus” operator (:=).

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All labels observed (3)

Label	Occurrences
Assignment Expressions canonical	1
Python Language Reference – Expressions – Assignment expressions	1
walrus operator	1

Statements (43)

Predicate	Object
instanceOf	Python language feature ⓘ expression construct ⓘ
alsoKnownAs	Assignment Expressions ⓘ surface form: walrus operator PEP 572 ⓘ surface form: walrus operator (:=)
author	Chris Angelico ⓘ
bdfLDecisionBy	Guido van Rossum ⓘ
bindingTime	at runtime during expression evaluation ⓘ
canBeUsedIn	comprehensions ⓘ generator expressions ⓘ if statements ⓘ lambda expressions (with restrictions) ⓘ while statements ⓘ
cannotTarget	attribute references in some contexts (subject to normal assignment rules) ⓘ
category	Python expression syntax ⓘ
controversy	PEP 572 ⓘ surface form: PEP 572 sparked significant discussion in the Python community
designGoal	avoid repeated expensive computations ⓘ improve readability in some patterns ⓘ
documentationSection	Assignment Expressions self-linksurface differs ⓘ surface form: Python Language Reference – Expressions – Assignment expressions
enables	inline assignment ⓘ reusing computed values within an expression ⓘ
evaluationOrder	expression on right of := is evaluated then bound to target name ⓘ
example	if (n := len(items)) > 0: print(n) ⓘ results = [y for x in data if (y := f(x)) is not None] ⓘ while (line := file.readline()) != "": process(line) ⓘ
exampleUseCase	capturing match results from regular expressions ⓘ filtering and binding in list comprehensions ⓘ reading input in a while loop ⓘ
introducedBy	PEP 572 ⓘ
introducedInVersion	Python 3.8 ⓘ
language	Python ⓘ
notAllowedIn	simple assignment target list ⓘ top-level of comprehension iterable expression (to avoid scoping confusion) ⓘ
pepNumber	572 ⓘ
purpose	assign values as part of larger expressions ⓘ
reduces	need for separate assignment statements ⓘ
relatedTo	assignment statements ⓘ name binding ⓘ
returns	assigned value ⓘ
scopeRule	follows normal Python scoping rules for the target name ⓘ
standardizedIn	Python 3 language specification ⓘ
status	accepted PEP ⓘ
syntaxForm	NAME := expression ⓘ
usesOperator	:= ⓘ

Referenced by (3)

Full triples — surface form annotated when it differs from this entity's canonical label.

PEP 572 → title → Assignment Expressions ⓘ

Assignment Expressions → alsoKnownAs → Assignment Expressions ⓘ

this entity surface form: walrus operator

Assignment Expressions → documentationSection → Assignment Expressions self-linksurface differs ⓘ

this entity surface form: Python Language Reference – Expressions – Assignment expressions