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From: Nathan Hilterbrand <nhilterbrand@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Powerful perl paradigm I don't find in python
Date: Fri, 15 Jan 2016 11:54:35 -0500
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On 01/15/2016 04:24 AM, Charles T. Smith wrote:
> while ($str != $tail) {
>      $str ~= s/^(head-pattern)//;
>      use ($1);
> }

IDK...  maybe the OP is looking for something like this? :

import re

def do_something(matchobj):
     print("I found {}".format(matchobj.group(0)))
     return ""

tail = "END"
str = "FeeFieFooFumEND"
pattern = r"F.."

while(str and str != tail):
     oldstr = str
     str = re.sub(pattern, do_something, str, 1)
     if str == oldstr:
         break


Though I would probably change the perl code, too:

while ($str and $str != $tail) {
     $str ~= s/^(head-pattern)//;
     if ($1) {
        do_something($1);
     } else {
        last;
     }
}

Otherwise there is too much risk of an infinite loop if the string is 
(1) empty, or (2) never ends up being equal to "tail"

Nathan