python regex to extract pattern

Question

I want to extract the digits 4699183 from the string query=regionID%3D4699183&c=1 but it's not working:

>>> import re
>>> string = 'query=regionID%3D4699183&c=1'
>>> string = re.sub("^(regionID%3D\d+)", "", string)
>>> string
'query=regionID%3D4699183&c=1'

How should I do it?

Cairnarvon · Accepted Answer · 2013-06-04 01:46:43Z

2

^(regionID%3D\d+) matches regionID%3D\d+ at the beginning of your string, which is not where it is in the actual string you provide. Even if it worked as you expected, though, you'd just be removing the whole thing, which obviously isn't what you want.

Try this instead:

>>> import re
>>> s = 'query=regionID%3D4699183&c=1'
>>> m = re.search(r'regionID%3D(\d+)', s)
>>> m.group(1)
'4699183'

This uses a capturing group to match one or more digits (greedily) after regionID%3D anywhere in your string.

answered Jun 4, 2013 at 1:46

Cairnarvon

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Comments

perreal · Accepted Answer · 2013-06-04 02:58:35Z

1

You are asking a match that starts with region while your input starts with query. Try this:

string = re.sub("^.*regionID%3D(\d+).*", r'\1', string)

It is also possible to do this without using regex, but this method may fail if you have other types of strings to test:

string = string.split('%3D')[1].split('&')[0]

Or you can use re.seach as suggested by Cairnarvon.

edited Jun 4, 2013 at 2:58

answered Jun 4, 2013 at 1:44

perreal

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1 Comment

Cairnarvon Over a year ago

Using regex substitution when you really just want to match a substring is pretty odd, though.

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