expanding regex in Python

Question

My program takes in a regex for describing a set of devices. For example,

--device=dev{01,02}{nyc}.hukka.com

should expand to dev01nyc.hukka.com and dev02nyc.hukka.com

How can I use the re module in Python to expand the user provided regex to complete strings that I can use? I am using Python 2.4.

This probably isn't possible. Regular expressions in general can accept languages that have an infinite amount of words, so RE libraries don't usually support trying to enumerate them. — millimoose
– millimoose, Commented Jan 11, 2012 at 21:00
You are essentially creating a new templating language. Be sure you really want that. unutbu does have the appropriate approach. — sleeplessnerd
– sleeplessnerd, Commented Jan 11, 2012 at 21:40

unutbu · Accepted Answer · 2012-01-11 21:31:21Z

6

If we re.split on the braces, we get:

In [7]: re.split(r'\{(.*?)\}',userstring)
Out[7]: ['--device=dev', '01,02', '', 'nyc', '.hukka.com']

Every other item in the list came from inside braces, which we next need to split on commas:

In [8]: [ part.split(',') if i%2 else [part]  for i,part in enumerate(re.split(r'\{(.*?)\}',userstring)) ]
Out[8]: [['--device=dev'], ['01', '02'], [''], ['nyc'], ['.hukka.com']]

Now we can use itertools.product to enumerate the possibilities:

import re
import itertools

userstring = '--device=dev{01,02}{nyc}.hukka.com'

for x in itertools.product(*[ part.split(',') if i%2 else [part]  for i,part in
                              enumerate(re.split(r'\{(.*?)\}',userstring)) ]):
    print(''.join(x))

yields

--device=dev01nyc.hukka.com
--device=dev02nyc.hukka.com

edited Jan 11, 2012 at 21:31

answered Jan 11, 2012 at 21:13

unutbu

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Loïc G. · Accepted Answer · 2012-01-11 21:22:28Z

2

Simply by extract the first braces to a group and iterate over this group :

import re

user_arg = "dev{01,02}{nyc}.hukka.com"

regex = re.compile('dev{(?P<dev_id>[^}]*)}{(nyc)}.hukka.com')
result = regex.search(user_arg)

devices = []
for dev_id in result.group(1).split(',') :
    devices.append("dev%s%s.hukka.com" % (dev_id, result.group(2)))

print devices

That returns :

$ ['dev01nyc.hukka.com', 'dev02nyc.hukka.com']

answered Jan 11, 2012 at 21:22

Loïc G.

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