Capturing repeating subpatterns in Python regex

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Capturing repeating subpatterns in Python regex

While matching an email address, after I match something like yasar@webmail, I want to capture one or more of (.w+)(what I am doing is a little bit more complicated, this is just an example), I tried adding (.w+)+ , but it only captures last match. For example, yasar@webmail.something.edu.tr matches but only include .tr after yasar@webmail part, so I lost .something and .edu groups. Can I do this in Python regular expressions, or would you suggest matching everything at first, and split the subpatterns later?

Asked By: yasar

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Answer #1:

re module doesn’t support repeated captures (regex supports it):

>>> m = regex.match(r'([.w]+)@((w+)(.w+)+)', 'yasar@webmail.something.edu.tr')
>>> m.groups()
('yasar', 'webmail.something.edu.tr', 'webmail', '.tr')
>>> m.captures(4)
['.something', '.edu', '.tr']

In your case I’d go with splitting the repeated subpatterns later. It leads to a simple and readable code e.g., see the code in @Li-aung Yip’s answer.

Answered By: jfs

Answer #2:

This will work:

>>> regexp = r"[w.]+@(w+)(.w+)?(.w+)?(.w+)?(.w+)?(.w+)?"
>>> email_address = "william.adama@galactica.caprica.fleet.mil"
>>> m = re.match(regexp, email_address)
>>> m.groups()
('galactica', '.caprica', '.fleet', '.mil', None, None)

But it’s limited to a maximum of six subgroups. A better way to do this would be:

>>> m = re.match(r"[w.]+@(.+)", email_address)
>>> m.groups()
('galactica.caprica.fleet.mil',)
>>> m.group(1).split('.')
['galactica', 'caprica', 'fleet', 'mil']

Note that regexps are fine so long as the email addresses are simple – but there are all kinds of things that this will break for. See this question for a detailed treatment of email address regexes.

Answered By: Li-aung Yip

Answer #3:

You can fix the problem of (.w+)+ only capturing the last match by doing this instead: ((?:.w+)+)

Answered By: Taymon

Answer #4:

This is what you are looking for:

>>> import re
>>> s="yasar@webmail.something.edu.tr"
>>> r=re.compile(".w+")
>>> m=r.findall(s)
>>> m
['.something', '.edu', '.tr']
Answered By: Tushar Vazirani
The answers/resolutions are collected from stackoverflow, are licensed under cc by-sa 2.5 , cc by-sa 3.0 and cc by-sa 4.0 .

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