[issue22687] horrible performance of textwrap.wrap() with a long word
Roundup Robot added the comment: New changeset 7bd87a219813 by Serhiy Storchaka in branch 'default': Issue #22687: Fixed some corner cases in breaking words in tetxtwrap. https://hg.python.org/cpython/rev/7bd87a219813 -- nosy: +python-dev ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Changes by Serhiy Storchaka storch...@gmail.com: -- resolution: - fixed stage: patch review - resolved status: open - closed ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: wordsplit_3.patch is wordsplit_2.patch with few added comments in tests. Is it enough? -- Added file: http://bugs.python.org/file38149/wordsplit_3.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: Ping. What can I do to move this issue forward? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: So what the patch (with mitigated tests) is more preferable? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
Here is a patch which is closer to current code but solves complexity issue and
also fixes some bugs in current code.
$ ./python -c import textwrap; print(textwrap.wrap('this-is-a-useful-feature',
width=1, break_long_words=False))
['this-', 'is-a', '-useful-', 'feature']
$ ./python -c import textwrap; print(textwrap.wrap('what-d\x27you-call-it.',
width=1, break_long_words=False))
['what-d', 'you-, 'call-', 'it.']
--
versions: +Python 2.7, Python 3.4
Added file: http://bugs.python.org/file37188/wordsplit.patch
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[issue22687] horrible performance of textwrap.wrap() with a long word
Georg Brandl added the comment: LGTM. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment:
I don't understand:
+expect = (this-|is-a-useful-|feature-|for-|
+ reformatting-|posts-|from-|tim-|peters'ly).split('|')
+self.check_wrap(text, 1, expect, break_long_words=False)
+self.check_split(text, expect)
Why would is-a-useful remain unsplit? It looks like you're making up new
rules.
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[issue22687] horrible performance of textwrap.wrap() with a long word
Changes by Antoine Pitrou pit...@free.fr: -- versions: -Python 2.7, Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
This is old rule. \w{2,}-(?=\w{2,} -- single letter shouldn't be separated. But
there was a bug in such simple regex, it splits a word after non-word character
(in particular apostrophe or hyphen) if it followed by word characters and
hyphen. There were attempts to fix this bug in issue596434 and issue965425 but
they missed a cases when non-word character is occurred inside a word.
Originally I had assigned this issue only to 3.5 because I supposed that the
solution needs either new features in re or backward-incompatible changes to
word splitting algorithm. But found solution doesn't require 3.5-only features,
doesn't change interface, and fixes performance and behavior bugs. So I think
it should be applied to maintained releases too.
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[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment:
This is old rule. \w{2,}-(?=\w{2,} -- single letter shouldn't be separated.
I don't agree. This was an implementation detail. There was no test, and it
wasn't specified anywhere.
If you think single letter shouldn't be separated, there should be some
grammatical or typographical reference on the Internet to prove it.
There were attempts to fix this bug in issue596434 and issue965425
Those don't seem related to single letters between hyphens.
But found solution doesn't require 3.5-only features, doesn't change
interface, and fixes performance and behavior bugs.
It does change behaviour in ways that could break existing code. The textwrap
behaviour is underspecified so it's not ok to assume that previous behaviour
was obviously buggy.
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[issue22687] horrible performance of textwrap.wrap() with a long word
R. David Murray added the comment: https://owl.english.purdue.edu/owl/resource/576/01/ Rule 8. So, no, in the middle of the word single letters aren't a problem, only at the beginning or the end of the word. -- nosy: +r.david.murray ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: Thank you David. If splitting single letter surrounded with hyphens is desirable, here is more complicated patch which does this. It deviates from original code more, but it doesn't look break any reasonable example. The textwrap behaviour is underspecified so it's not ok to assume that previous behaviour was obviously buggy. Aren't ['this-', 'is-a', '-useful-', 'feature'] and ['what-d', 'you-, 'call-', 'it.'] obvious bugs? -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Changes by Serhiy Storchaka storch...@gmail.com: Added file: http://bugs.python.org/file37190/wordsplit_2.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: To clarify, I would be fine with the previous patch if it didn't add the tests. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: Aren't ['this-', 'is-a', '-useful-', 'feature'] and ['what-d', 'you-, 'call-', 'it.'] obvious bugs? Obvious according to which rules? If we want to improve the behaviour of textwrap, IMHO it should be in a separate issue. And someone would have to study the word-wrapping rules of the English language :-) -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
R. David Murray added the comment: What I usually do in cases like this is to add the tests but mark them with comments saying that the tests test current behavior but are not testing parts of the (currently defined) API. That way you know if a change changes behavior and then can decide if that is a problem or not, as opposed to inadvertently changing behavior and only finding out when the bug reports roll in :) But yeah, defining the rules textwrap should follow is a different issue than the performance issue. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: To clarify, I would be fine with the previous patch if it didn't add the tests. The absent of tests could cause introducing new non-detected bugs and reappearing old bugs. Obvious according to which rules? If you think a word should be splitted before hyphen or apostrophe, there should be some grammatical or typographical reference on the Internet to prove it. I would be fine with moving the fix of textwrap behavior to a separate issue, but what to do with this issue then? We have not a patch which only fixes performance complexity and doesn't change the behavior. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: What I usually do in cases like this is to add the tests but mark them with comments saying that the tests test current behavior but are not testing parts of the (currently defined) API. That way you know if a change changes behavior and then can decide if that is a problem or not, as opposed to inadvertently changing behavior and only finding out when the bug reports roll in :) That's a good idea! -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
Current regex produces insane result.
$ ./python -c import textwrap; print(textwrap.wrap('this-is-a-useful-feature',
width=1, break_long_words=False))
['this-', 'is-a', '-useful-', 'feature']
Antoine's regex produces more correct result for this case: ['this-', 'is-',
'a-', 'useful-', 'feature']. But this is not totally correct, one-letter word
should not be separated. This can be easy fixed.
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[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: But this is not totally correct, one-letter word should not be separated. Why not? I guess it depends on English's rules for word splitting, which I don't know. In any case, this issue is not about improving correctness, only performance. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
Why not? I guess it depends on English's rules for word splitting, which I
don't know.
I suppose this is common rule in many languages. And current code supports it
(there is a special code in the regex to ensure this rule).
In any case, this issue is not about improving correctness,
only performance.
But the patch shouldn't add a regression.
$ ./python -c import textwrap; print(textwrap.wrap('this-is-a-useful',
width=1, break_long_words=False))
Current code: ['this-', 'is-a-useful']
Patched: ['this-', 'is-', 'a-', 'useful']
Just use lookahead assertion to ensure that the hyphen is followed by at least
two letters.
My previous message is about that current code is not always correct so it is
acceptable to replace it with not absolutely equivalent code.
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[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: I suppose this is common rule in many languages. I frankly don't know about this rule. And the tests don't check for it, so for me it's not broken. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
Tests are not perfect. But this is intentional design. The part of initial
regex:
r'\w{2,}-(?=\w{2,})|' # hyphenated words
Now it is more complicated. Note '(?=\w{2,})'.
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[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: Here is a patch which solves the algorithmic complexity issue by using a different scheme: instead of splitting, match words incrementally. -- keywords: +patch nosy: +pitrou stage: needs patch - patch review versions: -Python 2.7, Python 3.4 Added file: http://bugs.python.org/file37179/wordsplit_complexity.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: Actually, it is enough to change the regexp while still using re.split(). Updated patch attached. -- Added file: http://bugs.python.org/file37180/wordsplit_complexity2.patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: Unfortunately there are two disadvantages: 1. wordsep_re and wordsep_simple_re are public attributes and user code can depend on this. Changing their is a way to customize TextWrapper. 2. This is slowdown common case (no abnormally long words): $ ./python -m timeit -s 'import textwrap; s = abcde * 10**4' -- 'textwrap.wrap(s)' Unpatched: 178 msec per loop Patched: 285 msec per loop First reason stopped me from writing a patch. When change the way how to split words, I suggest to use undocumented re scanner. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: Are you sure? I get the reverse results here (second patch): Unpatched: $ ./python -m timeit -s 'import textwrap; s = abcde * 10**4' -- 'textwrap.wrap(s)' 10 loops, best of 3: 27 msec per loop Patched: $ ./python -m timeit -s 'import textwrap; s = abcde * 10**4' -- 'textwrap.wrap(s)' 10 loops, best of 3: 19.2 msec per loop wordsep_re and wordsep_simple_re are public attributes and user code can depend on this. Changing their is a way to customize TextWrapper. With my second patch, that shouldn't be a problem. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment:
Oh, sorry, I tested your first patch. Your second patch is faster than current
code to me. But it changes behavior.
textwrap.wrap('1a-2b', width=5)
['1a-', '2b']
With the patch the result is ['1a-2', 'b'].
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[issue22687] horrible performance of textwrap.wrap() with a long word
Antoine Pitrou added the comment: Yes... but in both cases the result is nonsensical, and untested. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: Possessive quantifiers (issue433030) is not a panacea. They allow to speed up regular expressions, but the complexity is still quadratic. Antoine's patch makes the complexity linear. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: May be atomic grouping or possessive quantifiers (issue433030) will help with this issue. -- ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
New submission from Piotr Engelking: Wrapping a paragraph containing a long word takes a lot of time: $ time python3 -c 'import textwrap; textwrap.wrap(a * 2 ** 16)' real3m14.923s user3m14.792s sys 0m0.016s $ A straightforward replacement is 5000 times faster: $ time python3 -c '(.join(x) for x in zip(*[iter(a * 2 ** 16)] * 70))' real0m0.053s user0m0.032s sys 0m0.016s $ Tested on Debian with python3.4 3.4.2-1 and python2.7 2.7.8-10. -- messages: 229768 nosy: inkerman priority: normal severity: normal status: open title: horrible performance of textwrap.wrap() with a long word type: performance versions: Python 2.7, Python 3.4 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Changes by Serhiy Storchaka storch...@gmail.com: -- nosy: +georg.brandl, serhiy.storchaka versions: +Python 3.5 ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Serhiy Storchaka added the comment: This particular case is related to the behavior of the wordsep_re regular expression in worst case. When text contains long sequence of words characters which is not ended by a hypen, or long sequence of non-word and non-space characters (and in some other cases), computational complexity of this regular expression matching is quadratic. This is a peculiarity of current implementation of regular expression engine. May be it is possible to rewrite the regular expression so that quadratic complexity will gone, but this is not so easy. The workaround -- use break_on_hyphens=False. -- assignee: - serhiy.storchaka priority: normal - low stage: - needs patch ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue22687] horrible performance of textwrap.wrap() with a long word
Changes by Ben Roberts bjr.robe...@gmail.com: -- nosy: +roippi ___ Python tracker rep...@bugs.python.org http://bugs.python.org/issue22687 ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
