https://github.com/python/cpython/commit/755cb49429581679fc7b12905cb3d3ecf43... commit: 755cb49429581679fc7b12905cb3d3ecf439032c branch: 3.8 author: Miss Islington (bot) <31488909+miss-islington@users.noreply.github.com> committer: GitHub <noreply@github.com> date: 2020-07-25T16:41:20-07:00 summary: bpo-39868: Add documentation for Assignment Expressions (walrus, PEP 572) (GH-18851) (cherry picked from commit f117cef25b5ffc4db9fbe373ddb65e14f59f0397) Co-authored-by: Shankar Jha <shankarj67@gmail.com> files: M Doc/reference/expressions.rst diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index 8036a491c29ab..18abce3c510bd 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: