[issue28029] Replace and empty strings
New submission from Stéphane Henriot:
A few days ago, the following behavior surprised me.
>>> "".replace("", "prefix", 1)
''
>>> "".replace("", "prefix")
'prefix'
It seems to me this edge case isn't correctly documented/implemented. I tested
with python 2.7, 3.4 and 3.5, I guess it applies for other versions as well.
Here are a few elements, for reference.
« string.replace(s, old, new[, maxreplace])
Return a copy of string s with all occurrences of substring old replaced by
new. If the optional argument maxreplace is given, the first maxreplace
occurrences are replaced. »
>>> "" in ""
True
>>> "".count("")
1
>>> "".find("")
0
https://hg.python.org/cpython/file/2.7/Objects/stringobject.c#l2750
https://hg.python.org/cpython/file/default/Objects/unicodeobject.c#l10479
Thanks,
Stéphane.
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messages: 275140
nosy: Stéphane Henriot
priority: normal
severity: normal
status: open
title: Replace and empty strings
type: behavior
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[issue28029] Replace and empty strings
Stéphane Henriot added the comment:
For what it's worth, here is the behavior in PyPy 2.2.1
>>>> "".replace("", "prefix", 1)
'prefix'
>>>> "".replace("", "prefix")
'prefix'
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[issue28029] Replace and empty strings
Stéphane Henriot added the comment:
Thanks for your help.
However, I'm not sure I would agree, regarding the correct behavior.
I guess the main question is « What is an occurrence? ».
Are you not convinced that in, count and find indicate occurrences?
To my understanding, the empty string occurs basically everywhere in strings
(including beginning and end):
>>> "blabla".replace("", "ε")
'εbεlεaεbεlεaε'
To give a bit more (useless?) context, I was implementing a GCD algorithm based
on replacements by Knuth (very beginning of TAOCP) and it looks like the
current cpython implementation gives 0 for gcd(1, 1) :(
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[issue28029] Replace and empty strings
Stéphane Henriot added the comment: I understand it might be a rather rare case. Nevertheless, don't you think the inconsistency Serhiy pointed out makes it look like a bug needing a fix? -- ___ Python tracker <http://bugs.python.org/issue28029> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
[issue28029] Replace and empty strings
Changes by Stéphane Henriot : -- nosy: +georg.brandl ___ Python tracker <http://bugs.python.org/issue28029> ___ ___ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
