Match exact two digits not more using regular expression

Question

Am trying to get date sting from filename using regular expression in a python script. Here is my date sting

'2012-09-25 ag.pdf'

To get date string from this filename am using this regex r'\d{4}[-]\d{1,2}[-]\d{1,2}' and it working fine

but some filenames also contains two digit year and for those am trying another regex r'\d{2}-\d{2}-\d{2}'

'2012-09-25 ag.pdf' also matches with second regex (r'\d{2}-\d{2}-\d{2}') pattern that causing issue with my script

How can i use regex in python to match exact two digits not more than that

Answer 1

You can create one regex for both cases:

^\d{2,4}-\d{1,2}-\d{1,2}

Demo: https://regex101.com/r/nZwZ58/4/

The good think about this first version is that is simpler and readable the bad thing is that will match a date with 3 digit.

The next one is more especific but more verbose.

^\d\d(\d\d)?-\d{1,2}-\d{1,2}

Demo: https://regex101.com/r/nZwZ58/3/

Answer 2

you have at least 3 options here:

First option: match the 4-digit year date first, and it matches, don't try to match the 2-digit year date.

Second option: modify your 2-digit year option to be more restrictive:

r'^\d{2}-\d{2}-\d{2}'

Third option: use match on the basename, not search. match tries to match from the start. If it finds 4 digits it will be a no-match.

Answer 3

Assuming that your date will always be at the start of the filename you could anchor your regex like so:

r'^\d{2}-\d{2}-\d{2}'

More docs here

EDIT: Could also use an or match:

r'^(\d{2}|\d{4})-\d{2}-\d{2}'

Answer 4

If Your filenames are always like this, you can prepend your regexp with ^ to match only on the beginning.