[New-bugs-announce] [issue41045] f-string's "debug" feature is undocumented

[Eric V. Smith]

New submission from Eric V. Smith <eric at trueblade.com>:

The feature of f-strings using '=' for "debugging" formatting is not documented.

>>> foo = 'bar'
>>> f'{foo=}'
"foo='bar'"


I'm not sure where this should fit in to the documentation, but it needs to be in there somewhere.

Basically the documentation needs to say:

1. The entire string from the opening brace { to the start of the expression appears in the output. This allows things like f'{foo = }' to evaluate to "foo = 'bar'" (notice the extra spaces).

2. If no format spec (like :20) is given, repr() is used on the expression. If a format spec is given, then str() is used on the expression. You can use repr() with a format spec by using the !r conversion, like: 

>>> f'{foo=:20}'
'foo=bar                 '

>>> f'{foo=!r:20}'
"foo='bar'               "

----------
assignee: docs at python
components: Documentation
messages: 371912
nosy: docs at python, eric.smith
priority: normal
severity: normal
stage: needs patch
status: open
title: f-string's "debug" feature is undocumented
versions: Python 3.10, Python 3.8, Python 3.9

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue41045>
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