[New-bugs-announce] [issue28516] contextlib.ExitStack.__enter__ has trivial but undocumented behavior

[Walker Hale IV]

New submission from Walker Hale IV:

contextlib.ExitStack implies but does not explicitly state that its __enter__ method trivially returns self.

This means that if a user invokes pop_all and then uses the resulting ExitStack instance in a with statement, the user will be relying on undocumented behavior. Avoiding undocumented behavior forces the user to instead use a tedious try/finally construct, partially defeating the elegance of context managers.

I propose that:

1. The ExitStack.__enter__ method be briefly mentioned as doing nothing besides returning self.

2. The example in pop_all documentation be expanded to show a following with statement that uses the new ExitStack instance.

The discussion in section 29.6.3.2 is not sufficient to make this trivial point clear.

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messages: 279296
nosy: Walker Hale IV
priority: normal
severity: normal
status: open
title: contextlib.ExitStack.__enter__ has trivial but undocumented behavior
versions: Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28516>
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