Éric Araujo added the comment: Thanks for the report. Would you be interested in experimenting and/or reading the code to find the anwser and propose a doc patch? ---------- keywords: +easy nosy: +eric.araujo stage: -> needs patch versions: +Python 2.7, Python 3.1, Python 3.2, Python 3.3 _______________________________________ Python tracker http://bugs.python.org/issue10713 _______________________________________

Ralph Corderoy added the comment: Examining the source of Ubuntu's python2.6 2.6.6-5ubuntu1 package suggests beyond the limits of the string is considered \W, like Perl. Modules/_sre.c: 336 LOCAL(int) 337 SRE_AT(SRE_STATE* state, SRE_CHAR* ptr, SRE_CODE at) 338 { 339 /* check if pointer is at given position */ 340 341 Py_ssize_t thisp, thatp; ... 365 case SRE_AT_BOUNDARY: 366 if (state->beginning == state->end) 367 return 0; 368 thatp = ((void*) ptr > state->beginning) ? 369 SRE_IS_WORD((int) ptr[-1]) : 0; 370 thisp = ((void*) ptr < state->end) ? 371 SRE_IS_WORD((int) ptr[0]) : 0; 372 return thisp != thatp; SRE_IS_WORD() returns 16 for the 63 \w characters, 0 otherwise. This is born out by tests. Note, 366 above confirms it's never true for an empty string. The documentation states that \B "is just the opposite of \b" yet re.match(r'\b', '') returns None and so does \B so \B isn't the opposite of \b in all cases. ---------- _______________________________________ Python tracker http://bugs.python.org/issue10713 _______________________________________

Martin Pool added the comment:

Note, 366 above confirms it's never true for an empty string. The documentation states that \B "is just the opposite of \b" yet re.match(r'\b', '') returns None and so does \B so \B isn't the opposite of \b in all cases.

This is also a bit strange if you follow the Perl line of reasoning of imagining there are non-word characters outside the string. And, indeed, in Perl, "" =~ /\B/ is true. So this patch adds some tests for \b behaviour and some docs. I think possible \B should actually change, but that would be a bigger (perhaps impossible?) change. ---------- keywords: +patch nosy: +poolie Added file: http://bugs.python.org/file22991/20110822-1604-re-docs.diff _______________________________________ Python tracker http://bugs.python.org/issue10713 _______________________________________

Éric Araujo added the comment: Like it. ---------- _______________________________________ Python tracker http://bugs.python.org/issue10713 _______________________________________

Ezio Melotti added the comment: Fixed, thanks for the patch! ---------- assignee: docs@python -> ezio.melotti resolution: -> fixed stage: patch review -> committed/rejected status: open -> closed _______________________________________ Python tracker http://bugs.python.org/issue10713 _______________________________________