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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Fri, 16 Dec 2011 10:57:06 -0700
Subject: Re: re.sub(): replace longest match instead of leftmost match?
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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. =A0Any suggestions?
>>
>> I'm working with IPv6 CIDR strings, and I want to replace the longest
>> match of "(0000:|0000$)+" with ":". =A0But when I use re.sub() it replac=
es
>> 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 =3D re.sub(r"\b0+(\d)\b", r"\1", string)

Close.

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

Cheers,
Ian