From f117cef25b5ffc4db9fbe373ddb65e14f59f0397 Mon Sep 17 00:00:00 2001 From: Shankar Jha Date: Sun, 26 Jul 2020 05:03:48 +0530 Subject: [PATCH] bpo-39868: Add documentation for Assignment Expressions (walrus, PEP 572) (#18851) --- Doc/reference/expressions.rst | 21 +++++++++++++++++++-- 1 file changed, 19 insertions(+), 2 deletions(-) diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index 8036a491c29..18abce3c510 100644 --- a/Doc/reference/expressions.rst +++ b/Doc/reference/expressions.rst @@ -1650,9 +1650,26 @@ Assignment expressions .. productionlist:: assignment_expression: [`identifier` ":="] `expression` -.. TODO: BPO-39868 +An assignment expression (sometimes also called a "named expression" or +"walrus") assigns an :token:`expression` to an :token:`identifier`, while also +returning the value of the :token:`expression`. -See :pep:`572` for more details about assignment expressions. +One common use case is when handling matched regular expressions: + +.. code-block:: python + + if matching := pattern.search(data): + do_something(matching) + +Or, when processing a file stream in chunks: + +.. code-block:: python + + while chunk := file.read(9000): + process(chunk) + +.. versionadded:: 3.8 + See :pep:`572` for more details about assignment expressions. .. _if_expr: