[issue40043] RegExp Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

[Matthew Barnett]

Matthew Barnett  added the comment:

That's what searching does!

Does the pattern match here? If not, advance by one character and try again. 
Repeat until a match is found or you've reached the end.

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[issue40043] RegExp Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

[Leon Hampton]

Leon Hampton  added the comment:

Matthew Barnett & SilentGhost,
Thank you for your prompt responses. (Really prompt. Amazing!)
SilentGhost,
Regarding your response, I used re.search, not re.match. When I used re.match, 
the regex failed. When I used re.search, it matched.
Here are my tests.

Your example (cut-and-pasted):
x = re.match(r'(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)', '|$)', '

I understand the re.match failing, since it always starts at the beginning of 
the string, but why did re.search succeed? After failing with the yes-pattern, 
when the regex engine backtracked to the (<)? did it decide not to match the 
'<' at all and skip the character? Seems like it. What do you think?

I am running Python 3.7 via Spyder 4.1.1 on Windows 10.

Respectfully,
Leon

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[issue40043] RegExp Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

[SilentGhost]

SilentGhost  added the comment:

Leon, this most likely is not a bug, not because what's stated in 
documentation, but because you're most likely not testing what you think you 
do. Here is the test that you should be doing:

>>> re.match(r'(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)', '>>

No match. If there is a different output in your setup, please provide both the 
output and the details of your system and Python installation.

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nosy: +SilentGhost
stage:  -> resolved
status: open -> closed

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[issue40043] RegExp Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

[Matthew Barnett]

Matthew Barnett  added the comment:

The documentation is talking about whether it'll match at the current position 
in the string. It's not a bug.

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resolution:  -> not a bug

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[issue40043] RegExp Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

[Leon Hampton]

Leon Hampton  added the comment:

Hello,
There may be a bug in the implementation of the Conditional Construction of 
Regular Expressions, namely the (?(id/name)yes-pattern|no-pattern).
In the Regular Expression documentation 
(https://docs.python.org/3.7/library/re.html), in the portion about the 
Conditional Construct, it gives this sample pattern 
'(<)?(\w+@\w+(?:\.\w+)+)(?(1)>|$)' and states that the pattern WILL NOT MATCH 
this string ' RegExp 
Conditional Construct (?(id/name)yes-pattern|no-pattern) Problem

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