Better way of writing this regex in Python

Question

Some string:

s = 'some text some text date may 04 at 05 AM some text some text'

I've written the regex to extract date from the above like below:

m = re.search(r'date ([a-z]{3} [0-9]{2}) at ([0-9]{2}) ([P][M])|date ([a-z]{3} [0-9]{2}) at ([0-9]{2}) ([A][M])', s)

Is it possible to write this regex in some shorter way or can '|' character be used in a better way than this? Because the above regexps are only different at 'AM' and 'PM' part. I just don't feel right using this regex.

1st thaught... `re.search(r'date ([a-z]{3} [0-9]{2}) at ([0-9]{2}) ([A|P][M]))', s) — Barun Sharma
– Barun Sharma, Commented Jul 22, 2015 at 9:46
@BarunSharma: It is such a common mistake to use | inside a character class. [A|P] matches A, | or P. — Wiktor Stribiżew
– Wiktor Stribiżew, Commented Jul 22, 2015 at 9:48

Wiktor Stribiżew · Accepted Answer · 2015-07-29 08:20:16Z

4

You can use

date ([a-z]{3} \d{2}) at (\d{2}) ([PA]M)

See demo

Compare your 2 alternatives:

date ([a-z]{3} [0-9]{2}) at ([0-9]{2}) ([P][M])
date ([a-z]{3} [0-9]{2}) at ([0-9]{2}) ([A][M])

Note how similar they are. We need to only add 1 alternative for PM or AM. It can be done by using a character class [PA] that will match either P or A.

Instead of [0-9], you can use shorthand class \d (it is a bit shorter :), and do not forget to declare the regex as a raw string with r'...').

Note I would use a case-insensitive flag re.I with this pattern (the pattern will match both pm and PM then).

edited Jul 29, 2015 at 8:20

answered Jul 22, 2015 at 9:45

Wiktor Stribiżew

631k41 gold badges502 silver badges632 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Better way of writing this regex in Python

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related