Regex groups in python

Question

I am trying to use regex to identify data of the format: XX days, XX hours, XX minutes (expecting minimal structural changes due to white spaces, comma and plurals) I wanted to see an effecient python way of using regex so that I can get numbers associated with days hours and minutes.

I tried the following:

matchingTime = "27 days, 21 hours, 23 minutes ago"
re.search('([0-9]{0,2}).*day.* ([0-9]+) .*hour.* ([0-9]+) .*minute.*',matchingTime)

For the above case it works fine and I get the values in group 1 2 3 respectively.

The issue is either of the field may not necessarily be present, say

matchingTime = "21 hours, 23 minutes ago"

for the above case it fails.

I do know I can get it done using trys and excepts, but I was hoping to find a concise and efficient way of doing it.

Any inputs will be really helpful. Would be glad to give any further clarifications to my query.

EDIT: [0-9]{0,2} for the days part, just trying a few ways to solve this.

Just put non-capturing parens then ? around the optional part '(:?([0-9]{0,2}).*day.* )?([0-9]+) .*hour.* ([0-9]+) .*minute.*' — Gene
– Gene, Commented Oct 8, 2013 at 16:33
You want to have optional groups have a look at python regex optional capture group — Rod
– Rod, Commented Oct 8, 2013 at 16:39

Jerry · Accepted Answer · 2013-10-08 16:40:22Z

2

You could perhaps use a regex like:

(?:(?P<days>[0-9]{0,2})\s*day[^, ]*,? *)?(?:(?P<hrs>[0-9]+)\s*hour[^, ]*,? *)?(?:(?P<min>[0-9]+)\s*minute[^, ]*,? *)?

regex101 demo

I'm using [^, ]*,? * for the optional commas and spaces and not using .* just so there's not too much backtracking.

I also used named capture groups and wrapped the whole groups for each day/hour/minute into a non-capture group, after which I put a ? to mark them as optional. Each group is fairly similar:

(?:                       # Start of non-capture group
    (?P<days>[0-9]{0,2})  # Numbers to capture
    \s*                   # Spaces if any
    day                   # Literal match
    [^, ]*,? *            # Anything until first comma and optional spaces
)?                        # Close of non-capture group and marking it as optional

edited Oct 8, 2013 at 16:40

answered Oct 8, 2013 at 16:34

Jerry

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3 Comments

falsetru Over a year ago

parenthesis is unbalanced.

Ajay Nair Over a year ago

So do I access the result in group 1 2 3 ?

Jerry Over a year ago

@AjayNair In a similar fashion to what you have, except you use the name of the capture as string. The match object with .group('days') for days, .group('hrs') for hours, etc

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