[New-bugs-announce] [issue44025] Match doc: Clarify '_' as a soft keyword

[Terry J. Reedy]

New submission from Terry J. Reedy <tjreedy at udel.edu>:

In #44010, we are trying, as best as is possible with comprehensible REs, to identify in which circumstances occurrences of 'match', 'case' and '_' are keywords, and should be marked as such.  I was initially unsure and even wrong about '_'.

1. Capture Patterns: I was confused by 'And is instead...'.  'It is instead ...', where 'it' refers to '_', is clearer to me.

2. Wildcard Patterns:  "'_' is a soft keyword" just says it sometimes is and sometimes is not, but not when, or rather, where.  After experiments like this (using the new IDLE 'copy with prompts' option ;-):

>>> _ = 'a'
>>> match [_, 'b']:
...     case [capture, _] if _ == 'a':
...         print(capture, _)
... 
a a

I added (in PR to come, with markup that might be improved)
"within any pattern, but only within patterns.  It is an identifier, as usual, even within ``match`` headers, ``guards``, and ``case blocks``.

Please consider also adding an example like the above.

----------
assignee: docs at python
components: Documentation
messages: 392848
nosy: brandtbucher, docs at python, gvanrossum, terry.reedy
priority: normal
severity: normal
stage: patch review
status: open
title: Match doc: Clarify '_' as a soft keyword
type: behavior
versions: Python 3.10, Python 3.11

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue44025>
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