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Title: [doc] Clarify exactly what \w matches in UNICODE mode
Type: enhancement Stage: needs patch
Components: Documentation, Regular Expressions Versions: Python 3.11, Python 3.10, Python 3.9
Status: open Resolution:
Dependencies: Superseder:
Assigned To: docs@python Nosy List: Andi McClure, docs@python, ezio.melotti, iritkatriel, mrabarnett, slateny, zwol
Priority: normal Keywords: easy

Created on 2015-11-27 15:50 by zwol, last changed 2022-04-11 14:58 by admin.

Messages (5)
msg255463 - (view) Author: Zack Weinberg (zwol) * Date: 2015-11-27 15:50
The `re` module documentation does not do a good job of explaining exactly what `\w` matches.  Quoting :

> \w
> For Unicode (str) patterns:
> Matches Unicode word characters; this includes most characters
> that can be part of a word in any language, as well as numbers
> and the underscore.

Empirically, this appears to mean "everything in Unicode general categories L* and N*, plus U+005F (underscore)".  That is a perfectly sensible definition and the documentation should state it in those terms.  "Unicode word characters" could mean any number of different things; note for instance that UTS#18 gives a very different definition.

(Further reading: plus links therefrom).
msg255464 - (view) Author: Andi McClure (Andi McClure) Date: 2015-11-27 16:14
I would like to request also a clear explanation be given for the documentation in the 2.7 branch. From :

"\w ... If UNICODE is set, this will match the characters [0-9_] plus whatever is classified as alphanumeric in the Unicode character properties database"

This is ambiguous. Does it mean the "Alphabetic" property from UAX#44? Does it mean something else?
msg255465 - (view) Author: Zack Weinberg (zwol) * Date: 2015-11-27 16:40
FWIW, the actual behavior of \w matching "everything in Unicode general categories L* and N*, plus U+005F (underscore)" is consistent across all versions I can conveniently test (2.7, 3.4, 3.5).

In 2.7, there are four characters in general category Nl that \w doesn't match, but I believe that is just a bug, not an intentional difference of behavior.
msg407440 - (view) Author: Irit Katriel (iritkatriel) * (Python committer) Date: 2021-12-01 11:03
It's too late for the 2.7 docs, but the current docs can still be updated.
msg414180 - (view) Author: Stanley (slateny) * Date: 2022-02-28 07:39
Would a change like this be accurate?

Matches Unicode word characters; this includes most alphanumeric characters as well as the underscore. In Unicode, alphanumeric characters are defined to be the general categories L + N (see If the :const:`ASCII` flag is used, only ``[a-zA-Z0-9_]`` is matched.
Date User Action Args
2022-04-11 14:58:24adminsetgithub: 69929
2022-02-28 07:39:46slatenysetnosy: + slateny
messages: + msg414180
2021-12-01 11:03:39iritkatrielsetnosy: + iritkatriel
versions: + Python 3.9, Python 3.10, Python 3.11, - Python 2.7, Python 3.5, Python 3.6
messages: + msg407440

keywords: + easy
title: Clarify exactly what \w matches in UNICODE mode -> [doc] Clarify exactly what \w matches in UNICODE mode
2016-01-04 03:52:01ezio.melottisetversions: - Python 3.2, Python 3.3, Python 3.4
nosy: + ezio.melotti, mrabarnett

components: + Regular Expressions
type: enhancement
stage: needs patch
2015-11-27 16:40:30zwolsetmessages: + msg255465
2015-11-27 16:14:25Andi McCluresetnosy: + Andi McClure
messages: + msg255464
2015-11-27 15:50:58zwolcreate