Re: Possible re bug when using ".*"
On 2022-12-28 19:07:06 +, MRAB wrote:
> On 2022-12-28 18:42, Alexander Richert - NOAA Affiliate via Python-list
> wrote:
> > print(re.sub(".*", "replacement", "pattern"))
> > yields the output "replacementreplacement".
[...]
> It's not a bug, it's a change in behaviour to bring it more into line with
> other regex implementations in other languages.
Interesting. Perl does indeed behave that way, too. Never noticed that
in 28 years of using it.
hp
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Re: Possible re bug when using ".*"
On 12/28/22 11:07, MRAB wrote:
On 2022-12-28 18:42, Alexander Richert - NOAA Affiliate via Python-list wrote:
In a couple recent versions of Python (including 3.8 and 3.10), the
following code:
import re
print(re.sub(".*", "replacement", "pattern"))
yields the output "replacementreplacement".
This behavior does not occur in 3.6.
Which behavior is the desired one? Perhaps relatedly, I noticed that even
in 3.6, the code
print(re.findall(".*","pattern"))
yields ['pattern',''] which is not what I was expecting.
It's not a bug, it's a change in behaviour to bring it more into line with
other regex implementations in other languages.
The new behavior makes no sense to me, but better to be consistent with the other regex engines than not -- I still get
thrown off by vim's regex.
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Re: Possible re bug when using ".*"
On 2022-12-28 18:42, Alexander Richert - NOAA Affiliate via Python-list
wrote:
In a couple recent versions of Python (including 3.8 and 3.10), the
following code:
import re
print(re.sub(".*", "replacement", "pattern"))
yields the output "replacementreplacement".
This behavior does not occur in 3.6.
Which behavior is the desired one? Perhaps relatedly, I noticed that even
in 3.6, the code
print(re.findall(".*","pattern"))
yields ['pattern',''] which is not what I was expecting.
It's not a bug, it's a change in behaviour to bring it more into line
with other regex implementations in other languages.
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Re: Possible re bug when using ".*"
Roel Schroeven schreef op 28/12/2022 om 19:59:
Alexander Richert - NOAA Affiliate via Python-list schreef op
28/12/2022 om 19:42:
In a couple recent versions of Python (including 3.8 and 3.10), the
following code:
import re
print(re.sub(".*", "replacement", "pattern"))
yields the output "replacementreplacement".
This behavior does not occur in 3.6.
Which behavior is the desired one? Perhaps relatedly, I noticed that even
in 3.6, the code
print(re.findall(".*","pattern"))
yields ['pattern',''] which is not what I was expecting.
The documentation for re.sub() and re.findall() has these notes:
"Changed in version 3.7: Empty matches for the pattern are replaced
when adjacent to a previous non-empty match." and "Changed in version
3.7: Non-empty matches can now start just after a previous empty match."
That's probably describes the behavior you're seeing. ".*" first
matches "pattern", which is a non-empty match; then it matches the
empty string at the end, which is an empty match but is replaced
because it is adjacent to a non-empty match.
Seems somewhat counter-intuitive to me, but AFAICS it's the intended
behavior.
For what it's worth, there's some discussion about this in this Github
issue: https://github.com/python/cpython/issues/76489
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Re: Possible re bug when using ".*"
Alexander Richert - NOAA Affiliate via Python-list schreef op 28/12/2022
om 19:42:
In a couple recent versions of Python (including 3.8 and 3.10), the
following code:
import re
print(re.sub(".*", "replacement", "pattern"))
yields the output "replacementreplacement".
This behavior does not occur in 3.6.
Which behavior is the desired one? Perhaps relatedly, I noticed that even
in 3.6, the code
print(re.findall(".*","pattern"))
yields ['pattern',''] which is not what I was expecting.
The documentation for re.sub() and re.findall() has these notes:
"Changed in version 3.7: Empty matches for the pattern are replaced when
adjacent to a previous non-empty match." and "Changed in version 3.7:
Non-empty matches can now start just after a previous empty match."
That's probably describes the behavior you're seeing. ".*" first matches
"pattern", which is a non-empty match; then it matches the empty string
at the end, which is an empty match but is replaced because it is
adjacent to a non-empty match.
Seems somewhat counter-intuitive to me, but AFAICS it's the intended
behavior.
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Possible re bug when using ".*"
In a couple recent versions of Python (including 3.8 and 3.10), the
following code:
import re
print(re.sub(".*", "replacement", "pattern"))
yields the output "replacementreplacement".
This behavior does not occur in 3.6.
Which behavior is the desired one? Perhaps relatedly, I noticed that even
in 3.6, the code
print(re.findall(".*","pattern"))
yields ['pattern',''] which is not what I was expecting.
Thanks,
Alex Richert
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*RedLine Performance Systems*
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