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RE Question

I don't understand why the two REs produce a different result. I read
the RE guide but still I can't seem to figure it out.
t 'echo user=name password=pass path="/ret files"\r\n' re.findall(r'(? <=\s)[^=]+=((?:".*")|(?: \S*))(?=\s)', t) ['name', 'pass', '"/ret files"'] re.findall(r'(? <=\s)[^=]+=((".*")|(\S*) )(?=\s)', t)

[('name', '', 'name'), ('pass', '', 'pass'), ('"/ret files"', '"/ret
files"', '')]
Also, does '|' char (meaning or) produces a pair for each section. I
don't understand how it works. Can someone please direct me to a place
which will explain it?

Thanks.
Aug 18 '05 #1
3 1100
Yoav wrote:
I don't understand why the two REs produce a different result. I read
the RE guide but still I can't seem to figure it out.
>>> t 'echo user=name password=pass path="/ret files"\r\n' >>> re.findall(r'(? <=\s)[^=]+=((?:".*")|(?: \S*))(?=\s)', t) ['name', 'pass', '"/ret files"'] >>> re.findall(r'(? <=\s)[^=]+=((".*")|(\S*) )(?=\s)', t)
[('name', '', 'name'), ('pass', '', 'pass'), ('"/ret files"', '"/ret
files"', '')]


Hi Yoav.

You can see at "sre" documentation (use that instead of the docs for "re")
that using "?:" you're asking for a non-groupping version of the
parenthesis match. When you use parenthesis, the matched expression is
saved for using later. Using "?:" you prevent that. This is what causes
the difference for you.
Also, does '|' char (meaning or) produces a pair for each section. I
don't understand how it works. Can someone please direct me to a place
which will explain it?


I didn't get your second question. When you use "|" the first match is
used. It is a short-circuited version of "or". I mean, it tries the first
regexp, if it matches, the second expression is ignored. The same is true
for "and", except that the comparisons end on the first false result.
Be seeing you,
--
Jorge Godoy <go***@ieee.org >

Aug 18 '05 #2
Thanks, it seems like the first answer covers the second as well.

Thank you.

Jorge Godoy wrote:
Yoav wrote:

I don't understand why the two REs produce a different result. I read
the RE guide but still I can't seem to figure it out.
>>> t

'echo user=name password=pass path="/ret files"\r\n'
>>> re.findall(r'(? <=\s)[^=]+=((?:".*")|(?: \S*))(?=\s)', t)

['name', 'pass', '"/ret files"']
>>> re.findall(r'(? <=\s)[^=]+=((".*")|(\S*) )(?=\s)', t)

[('name', '', 'name'), ('pass', '', 'pass'), ('"/ret files"', '"/ret
files"', '')]

Hi Yoav.

You can see at "sre" documentation (use that instead of the docs for "re")
that using "?:" you're asking for a non-groupping version of the
parenthesis match. When you use parenthesis, the matched expression is
saved for using later. Using "?:" you prevent that. This is what causes
the difference for you.

Also, does '|' char (meaning or) produces a pair for each section. I
don't understand how it works. Can someone please direct me to a place
which will explain it?

I didn't get your second question. When you use "|" the first match is
used. It is a short-circuited version of "or". I mean, it tries the first
regexp, if it matches, the second expression is ignored. The same is true
for "and", except that the comparisons end on the first false result.
Be seeing you,

Aug 18 '05 #3
What is the difference between the RE module and the SRE one?

-------- Original Message --------
From: Jorge Godoy <go***@ieee.org >
To:
Subject: Re:RE Question
Date: 18/8/2005 17:44
Yoav wrote:

I don't understand why the two REs produce a different result. I read
the RE guide but still I can't seem to figure it out.
>>> t

'echo user=name password=pass path="/ret files"\r\n'
>>> re.findall(r'(? <=\s)[^=]+=((?:".*")|(?: \S*))(?=\s)', t)

['name', 'pass', '"/ret files"']
>>> re.findall(r'(? <=\s)[^=]+=((".*")|(\S*) )(?=\s)', t)

[('name', '', 'name'), ('pass', '', 'pass'), ('"/ret files"', '"/ret
files"', '')]

Hi Yoav.

You can see at "sre" documentation (use that instead of the docs for "re")
that using "?:" you're asking for a non-groupping version of the
parenthesis match. When you use parenthesis, the matched expression is
saved for using later. Using "?:" you prevent that. This is what causes
the difference for you.

Also, does '|' char (meaning or) produces a pair for each section. I
don't understand how it works. Can someone please direct me to a place
which will explain it?

I didn't get your second question. When you use "|" the first match is
used. It is a short-circuited version of "or". I mean, it tries the first
regexp, if it matches, the second expression is ignored. The same is true
for "and", except that the comparisons end on the first false result.
Be seeing you,

Aug 18 '05 #4

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