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Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example

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fl wrote:

> Hi,
> 
> This example is from the link:
> 
> https://wiki.python.org/moin/RegularExpression
> 
> 
> I have thought about it quite a while without a clue yet. I notice that it
> uses double quote ", in contrast to ' which I see more often until now.
> It looks very complicated to me. Could you simplified it to a simple
> example?

Just break it into its components.

"(...)" in the context of re.split() keeps the delimiters while just "..." 
does not. Example:

>>> re.split("a+", "abbaaababa")
['', 'bb', 'b', 'b', '']
>>> re.split("(a+)", "abbaaababa")
['', 'a', 'bb', 'aaa', 'b', 'a', 'b', 'a', '']

r"\(" matches the openening parenthesis. The "(" has to be escaped because 
it otherwise has a special meaning (begin group) in a regex.

"[abc]" matches a, b, or c. A leading ^ inverts the set, so "[^abc]" matches 
anything but a, b, or c. Therefore "[^)]" matches anything but the closing 
parenthesis.

The complete regex then is: match two opening parens, then one or more chars 
that are not closing parens, then two closing parens, and make the complete 
group part of the resulting list.

PS: Note that sometimes the re.DEBUG flag may be helpful in understanding 
noisy regexes:

subpattern 1 
  literal 40 
  literal 40 
  max_repeat 1 4294967295 
    not_literal 41 
  literal 41 
  literal 41 
<_sre.SRE_Pattern object at 0x7f5740455c90>

> import re
> split_up = re.split(r"(\(\([^)]+\)\))",
>                     "This is a ((test)) of the ((emergency broadcasting
>                     station.))")
> 
> 
> ...which produces:
> 
> 
> ["This is a ", "((test))", " of the ", "((emergency broadcasting
> [station.))" ]

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How to decipher :re.split(r"(\(\([^)]+\)\))" in the example fl <rxjwg98@gmail.com> - 2014-07-10 08:37 -0700
  Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Peter Otten <__peter__@web.de> - 2014-07-10 18:49 +0200
  Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example MRAB <python@mrabarnett.plus.com> - 2014-07-10 18:01 +0100
  Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Joel Goldstick <joel.goldstick@gmail.com> - 2014-07-10 13:05 -0400
  Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Albert-Jan Roskam <fomcl@yahoo.com> - 2014-07-10 12:15 -0700
  Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Cameron Simpson <cs@zip.com.au> - 2014-07-11 11:29 +1000
    Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Roy Smith <roy@panix.com> - 2014-07-10 22:18 -0400
      Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Tim Chase <python.list@tim.thechases.com> - 2014-07-10 21:37 -0500
        Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Roy Smith <roy@panix.com> - 2014-07-10 23:33 -0400
          Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Chris Angelico <rosuav@gmail.com> - 2014-07-11 14:31 +1000
          Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example alister <alister.nospam.ware@ntlworld.com> - 2014-07-11 08:00 +0000
          Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Steven D'Aprano <steve@pearwood.info> - 2014-07-11 09:04 +0000
            Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example Albert-Jan Roskam <fomcl@yahoo.com> - 2014-07-11 08:18 -0700

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