Python regex, match more than one integer

Question

The below code prints white space and not '11' and I can't figure out why. Replacing [0-9]* with [0-9]{1,2} prints '11'. Can any one help?

import re
test_string = 'cake_11xlfslijg'
pattern = '.*(?P<order>[0-9]*)'
result = re.compile(pattern).search(test_string)
if result:
    print 'result'
    print result.group('order')
else:
    print result

Replacing [0-9]* with [0-9]{1,2} prints 1, not 11.

Tim Pietzcker
– Tim Pietzcker

2011-07-20 15:04:49 +00:00
Commented Jul 20, 2011 at 15:04 — Tim Pietzcker
– Tim Pietzcker, Commented Jul 20, 2011 at 15:04

Tomalak · Accepted Answer · 2011-07-20 14:38:12Z

12

Try [0-9]+. The * translates to "zero or more", and there are zero or more digits right at the start of your string.

answered Jul 20, 2011 at 14:38

Tomalak

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3 Comments

jtniehof Over a year ago

Quick way to show this: re.search('(.*)(\d*)', 'cake11').groups()

Tim Pietzcker Over a year ago

This will still only match 1, not 11, because the regex engine backtracks only as far as needed.

Tomalak Over a year ago

@Tim Oh, I've seen the .* only now (that's why I also wrote "at the start of the string" instead of "at the end"). Of course you are right. The regex should be (?P<order>[0-9]+) without the .*.

Senthil Kumaran · Accepted Answer · 2011-07-20 14:42:29Z

7

Your regex should be this

pattern = '(?P<order>[0-9]+)'

Removed the first .* as it will do a greedy match of the entire string.
Made [0-9]+ as it will match the digits only even at least one is present, else it will return None.

answered Jul 20, 2011 at 14:42

Senthil Kumaran

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Comments

Kirill Polishchuk · Accepted Answer · 2011-07-20 14:38:36Z

1

Because * means: any number of repetitions, in your regex .* will match all the string, because . means any character, i.e. including [0-9]

answered Jul 20, 2011 at 14:38

Kirill Polishchuk

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Comments

eyquem · Accepted Answer · 2011-07-20 14:51:29Z

0

A regex pattern needs to have a minimum of anchors.

With '.' and '[0-9]' , there are only optional symbols.

Try

import re

for test_string in ( 'cake_11xlfslijg',
                     'cake_uuxlfslijg'):
    pattern = '.*?(?P<order>[0-9]+)'
    result = re.compile(pattern).search(test_string)
    print test_string
    print 'result: ',repr(result.group('order')) if result else result
    print

gives

cake_11xlfslijg
result:  '11'

cake_uuxlfslijg
result:  None

answered Jul 20, 2011 at 14:51

eyquem

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