Python regex match OR operator

Question

I'm trying to match time formats in AM or PM.

i.e. 02:40PM
     12:29AM

I'm using the following regex

timePattern = re.compile('\d{2}:\d{2}(AM|PM)')

but it keeps returning only AM PM string without the numbers. What's going wrong?

@Tommy: He is using a capturing group; that's what's causing the problem. When the regex has capturing groups, findall() returns only those, not the full match. — Alan Moore
– Alan Moore, Commented Nov 6, 2013 at 20:15
Mind you, you could also avoid the group entirely, changing (AM|PM) to [AP]M. — ShadowRanger
– ShadowRanger, Commented Dec 2, 2016 at 1:09

hwnd · Accepted Answer · 2013-11-06 20:14:20Z

42

Use a non capturing group (?: and reference to the match group.

Use re.I for case insensitive matching.

import re

def find_t(text):
    return re.search(r'\d{2}:\d{2}(?:am|pm)', text, re.I).group()

You can also use re.findall() for recursive matching.

def find_t(text):
    return re.findall(r'\d{2}:\d{2}(?:am|pm)', text, re.I)

See demo

edited Nov 6, 2013 at 20:14

answered Nov 6, 2013 at 20:09

hwnd

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score 7 · Accepted Answer · 2013-11-06 20:05:21Z

7

Use a non-delimited capture group (?:...):

>>> from re import findall
>>> mystr = """
... 02:40PM
... 12:29AM
... """
>>> findall("\d{2}:\d{2}(?:AM|PM)", mystr)
['02:40PM', '12:29AM']
>>>

Also, you can shorten your Regex to \d\d:\d\d(?:A|P)M.

edited Nov 6, 2013 at 20:05

answered Nov 6, 2013 at 19:56

user2555451

Comments

porges · Accepted Answer · 2013-11-06 19:57:56Z

4

It sounds like you're accessing group 1, when you need to be accessing group 0.

The groups in your regex are as follows:

\d{2}:\d{2}(AM|PM)
           |-----|  - group 1
|----------------|  - group 0 (always the match of the entire pattern)

You can access the entire match via:

timePattern.match('02:40PM').group(0)

answered Nov 6, 2013 at 19:57

porges

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Ashwini Chaudhary · Accepted Answer · 2013-11-06 19:56:19Z

2

You're not capturing the Hour, minute fields:

>>> import re
>>> r = re.compile('(\d{2}:\d{2}(?:AM|PM))')
>>> r.search('02:40PM').group()
'02:40PM'
>>> r.search('Time is 12:29AM').group()
'12:29AM'

answered Nov 6, 2013 at 19:56

Ashwini Chaudhary

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matt forsythe · Accepted Answer · 2013-11-06 19:56:46Z

2

Are you accidentally grabbing the 1st cluster (the stuff in that matches the portion of the pattern in the parentheses) instead of the "0st" cluster (which is the whole match)?

answered Nov 6, 2013 at 19:56

matt forsythe

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