Skip to content

[3.9] bpo-42669: Document that except rejects nested tuples (GH-23822) #23870

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

Merged
ericvsmith merged 1 commit into from
Dec 20, 2020
Merged

[3.9] bpo-42669: Document that except rejects nested tuples (GH-23822) #23870

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
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
bpo-42669: Document that except rejects nested tuples (GH-23822) 
In Python 2, it was possible to use `except` with a nested tuple, and occasionally natural.  For example, `zope.formlib.interfaces.InputErrors` is a tuple of several exception classes, and one might reasonably think to do something like this:

    try:
        self.getInputValue()
        return True
    except (InputErrors, SomethingElse):
        return False

As of Python 3.0, this raises `TypeError: catching classes that do not inherit from BaseException is not allowed` instead: one must instead either break it up into multiple `except` clauses or flatten the tuple.  However, the reference documentation was never updated to match this new restriction.  Make it clear that the definition is no longer recursive.

Automerge-Triggered-By: GH:ericvsmith
(cherry picked from commit c95f8bc)

Co-authored-by: Colin Watson <cjwatson@debian.org>
  • Loading branch information
@cjwatson @miss-islington
cjwatson authored and miss-islington committed Dec 20, 2020
commit 4bbad00ee8a85d0c209a424ec605f7fa11c89377
3 changes: 2 additions & 1 deletion Doc/reference/compound_stmts.rst
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -254,7 +254,8 @@ present, must be last; it matches any exception. For an except clause with an
expression, that expression is evaluated, and the clause matches the exception
if the resulting object is "compatible" with the exception. An object is
compatible with an exception if it is the class or a base class of the exception
object or a tuple containing an item compatible with the exception.
object, or a tuple containing an item that is the class or a base class of
the exception object.

If no except clause matches the exception, the search for an exception handler
continues in the surrounding code and on the invocation stack. [#]_
Expand Down
1 change: 1 addition & 0 deletions Misc/ACKS
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1829,6 +1829,7 @@ Zachary Ware
Barry Warsaw
Steve Waterbury
Bob Watson
Colin Watson
David Watson
Aaron Watters
Henrik Weber
Expand Down