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Re: re.sub(): replace longest match instead of leftmost match?

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On Fri, Dec 16, 2011 at 10:57 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote:
> On Fri, Dec 16, 2011 at 10:36 AM, MRAB <python@mrabarnett.plus.com> wrote:
>> On 16/12/2011 16:49, John Gordon wrote:
>>>
>>> According to the documentation on re.sub(), it replaces the leftmost
>>> matching pattern.
>>>
>>> However, I want to replace the *longest* matching pattern, which is
>>> not necessarily the leftmost match.  Any suggestions?
>>>
>>> I'm working with IPv6 CIDR strings, and I want to replace the longest
>>> match of "(0000:|0000$)+" with ":".  But when I use re.sub() it replaces
>>> the leftmost match, even if there is a longer match later in the string.
>>>
>>> I'm also looking for a regexp that will remove leading zeroes in each
>>> four-digit group, but will leave a single zero if the group was all
>>> zeroes.
>>>
>> How about this:
>>
>> result = re.sub(r"\b0+(\d)\b", r"\1", string)
>
> Close.
>
> pattern = r'\b0+([1-9a-f]+|0)\b'
> re.sub(pattern, r'\1', string, flags=re.IGNORECASE)

Doh, that's still not quite right.

pattern = r'\b0{1,3}([1-9a-f][0-9a-f]*|0)\b'
re.sub(pattern, r'\1', string, flags=re.IGNORECASE)

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re.sub(): replace longest match instead of leftmost match? John Gordon <gordon@panix.com> - 2011-12-16 16:49 +0000
  Re: re.sub(): replace longest match instead of leftmost match? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-12-16 11:56 -0500
    Re: re.sub(): replace longest match instead of leftmost match? John Gordon <gordon@panix.com> - 2011-12-16 21:04 +0000
      Re: re.sub(): replace longest match instead of leftmost match? MRAB <python@mrabarnett.plus.com> - 2011-12-16 21:36 +0000
        Re: re.sub(): replace longest match instead of leftmost match? Duncan Booth <duncan.booth@invalid.invalid> - 2011-12-19 15:46 +0000
  Re: re.sub(): replace longest match instead of leftmost match? MRAB <python@mrabarnett.plus.com> - 2011-12-16 17:36 +0000
  Re: re.sub(): replace longest match instead of leftmost match? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-16 10:57 -0700
  Re: re.sub(): replace longest match instead of leftmost match? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-16 10:59 -0700
    Re: re.sub(): replace longest match instead of leftmost match? John Gordon <gordon@panix.com> - 2011-12-16 21:06 +0000
  Re: re.sub(): replace longest match instead of leftmost match? MRAB <python@mrabarnett.plus.com> - 2011-12-16 18:19 +0000
  Re: re.sub(): replace longest match instead of leftmost match? Roy Smith <roy@panix.com> - 2011-12-16 13:36 -0500
    Re: re.sub(): replace longest match instead of leftmost match? John Gordon <gordon@panix.com> - 2011-12-16 21:07 +0000
    Re: re.sub(): replace longest match instead of leftmost match? Terry Reedy <tjreedy@udel.edu> - 2011-12-16 17:26 -0500
  Re: re.sub(): replace longest match instead of leftmost match? ting@thsu.org - 2011-12-19 15:15 -0800
    Re: re.sub(): replace longest match instead of leftmost match? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-19 19:58 -0700

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