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

Albert-Jan Roskam fomcl at yahoo.com
Fri Jul 11 17:18:09 CEST 2014



----- Original Message -----

> From: Steven D'Aprano <steve at pearwood.info>
> To: python-list at python.org
> Cc: 
> Sent: Friday, July 11, 2014 11:04 AM
> Subject: Re: How to decipher :re.split(r"(\(\([^)]+\)\))" in the example
> 
> On Thu, 10 Jul 2014 23:33:27 -0400, Roy Smith wrote:
> 
>>  In article <mailman.11747.1405046292.18130.python-list at python.org>,
>>   Tim Chase <python.list at tim.thechases.com> wrote:
>> 
>>>  On 2014-07-10 22:18, Roy Smith wrote:
>>>  > > Outside this are \( and \): these are literal opening 
> and closing
>>>  > > bracket characters. So:
>>>  > > 
>>>  > >    \(\([^)]+\)\)
>>>  >
>>>  > although, even better would be to use to utterly awesome
>>>  >> re.VERBOSE
>>>  > flag, and write it as:
>>>  > 
>>>  >      \({2} [^)]+ \){2}
>>> 
>>>  Or heck, use a multi-line verbose expression and comment it for
>>>  clarity:
>>> 
>>>    r = re.compile(r"""
>>>      (            # begin a capture group
>>>       \({2}       # two literal "(" characters [^)]+  
>      # one or more
>>>       non-close-paren characters \){2}       # two literal 
> ")"
>>>       characters
>>>      )            # close the capture group """, 
> re.VERBOSE)
>>> 
>>>  -tkc
>> 
>>  Ugh.  That reminds me of the classic commenting anti-pattern:
> 
> The sort of dead-simple commenting shown below is not just harmless but 
> can be *critically important* for beginners, who otherwise may not know 
> what "l = []" means.
> 
>>  l = []                  # create an empty list 
>>  for i in range(10):     # iterate over the first 10 integers
>>      l.append(i)         # append each one to the list
> 

Anything better than this hideous type of commenting: (?#...), e.g
>>> re.match("(19|20)[0-9]{2}(?#year)-[0-9]{2}(?#month)", "2010-12")
Same thing for the 'limsux' modifiers, although *maybe* they can be useful.



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