Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

gh-86482: Document assignment expression need for ()s #23291

Merged
merged 8 commits into from
Oct 6, 2022
Merged

gh-86482: Document assignment expression need for ()s #23291

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
8 commits
Select commit Hold shift + click to select a range
ff66b33
bpo-42316: Document assignment expression need for ()s
terryjreedy Nov 15, 2020
09653d7
Add 'be'
terryjreedy Nov 15, 2020
43ed4f5
Merge branch 'main' into walrus
JelleZijlstra Apr 5, 2022
b066b83
Merge branch 'main' into walrus
JelleZijlstra Oct 3, 2022
4d0a933
Apply suggestions from code review
JelleZijlstra Oct 3, 2022
ae4788e
Update Doc/reference/expressions.rst
JelleZijlstra Oct 3, 2022
07b9fe5
Update Doc/reference/expressions.rst
JelleZijlstra Oct 3, 2022
a9d94bf
Update Doc/reference/expressions.rst
JelleZijlstra Oct 3, 2022
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
7 changes: 7 additions & 0 deletions Doc/reference/expressions.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1766,6 +1766,13 @@ Or, when processing a file stream in chunks:
while chunk := file.read(9000):
process(chunk)

Assignment expressions must be surrounded by parentheses when used
as sub-expressions in slicing, conditional, lambda,
Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Unparenthesized assignment expressions in slices were implemented in #23317, so they are allowed since 3.10. Also, assignment expression need to parenthesized in assert and with statements.

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Unparenthesized walruses are allowed in index expressions but not slices. This is current 3.12:

>>> x[y:=3]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> x[y:=3:z:=4]
  File "<stdin>", line 1
    x[y:=3:z:=4]
          ^
SyntaxError: invalid syntax

Copy link
Member

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

Correct! I mixed up indexes/slices. Sorry!

keyword-argument, and comprehension-if expressions
and in ``assert`` and ``with`` statements.
In all other places where they can be used, parentheses are not required,
including in ``if`` and ``while`` statements.

.. versionadded:: 3.8
See :pep:`572` for more details about assignment expressions.

Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2020-11-15-02-08-43.bpo-42316.LqdkWK.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1 @@
Document some places where an assignment expression needs parentheses.