Re: Powerful perl paradigm I don't find in python

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From	Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de>
Newsgroups	comp.lang.python
Subject	Re: Powerful perl paradigm I don't find in python
Date	Fri, 15 Jan 2016 14:20:17 +0100
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On 15.01.2016 12:04, Charles T. Smith wrote:
> On Fri, 15 Jan 2016 11:42:24 +0100, Wolfgang Maier wrote:
>
>> On 15.01.2016 10:43, Peter Otten wrote:
>>> Charles T. Smith wrote:
>>>
>>>> while ($str != $tail) {
>>>>       $str ~= s/^(head-pattern)//;
>>>>       use ($1);
>>>> }
>>>
> ....
>>
>> things = []
>> while some_str != tail:
>>       m = re.match(pattern_str, some_str)
>>       things.append(some_str[:m.end()])
>>       some_str = some_str[m.end():]
>>
>> # do something with things
>
>
> Okay, I guess it's not a lot more work to use the end() method to manually
> cut out the found portion.
>
> What the original snippet does is parse *and consume* a string - actually,
> to avoid maintaining a cursor traverse the string.  The perl feature is that
> substitute allows the found pattern to be replaced, but retains the group
> after the expression is complete.
>
> The end() method is actually such a cursor, but already set up for you
> by the class, and then the slicing considerably simplifies its use.
>

I see. If consuming the string is not essential for you, but just a 
handy trick to avoid the cursor, you may prefer this (most likely 
faster) solution:

pattern = pattern_str.compile()
try:
     matches = pattern.findall(some_str, endpos=some_str.index(tail))
except ValueError:
     # do something if tail is not found
     pass

Best,
Wolfgang

Thread

Powerful perl paradigm I don't find in python "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-01-15 09:24 +0000
  Re: Powerful perl paradigm I don't find in python Peter Otten <__peter__@web.de> - 2016-01-15 10:43 +0100
    Re: Powerful perl paradigm I don't find in python Michael Vilain <vilain@NOspamcop.net> - 2016-01-15 02:20 -0800
  Re: Powerful perl paradigm I don't find in python Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2016-01-15 11:42 +0100
    Re: Powerful perl paradigm I don't find in python "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-01-15 11:04 +0000
      Re: Powerful perl paradigm I don't find in python "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-01-15 11:06 +0000
      Re: Powerful perl paradigm I don't find in python Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2016-01-15 14:20 +0100
        Re: Powerful perl paradigm I don't find in python "Charles T. Smith" <cts.private.yahoo@gmail.com> - 2016-01-18 13:05 +0000
          Re: Powerful perl paradigm I don't find in python Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2016-01-18 14:33 +0100
      Re: Powerful perl paradigm I don't find in python Peter Otten <__peter__@web.de> - 2016-01-15 14:34 +0100
  Re: Powerful perl paradigm I don't find in python Ulli Horlacher <framstag@rus.uni-stuttgart.de> - 2016-01-15 13:51 +0000
    Re: Powerful perl paradigm I don't find in python me <self@example.org> - 2016-01-15 15:20 +0000
  Re: Powerful perl paradigm I don't find in python Nathan Hilterbrand <nhilterbrand@gmail.com> - 2016-01-15 11:54 -0500

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