Re: [Tutor] regular expression question

[Mike Hall]

Sorry, my last reply crossed this one (and yes, I forgot again to CC 
the list).
I'm experimenting now with your use of the "or" operator( "|") between 
two expressions, thanks.


On Mar 8, 2005, at 6:42 PM, Danny Yoo wrote:

On Tue, 8 Mar 2005, Mike Hall wrote:
Yes, my existing regex is using a look behind assertion:
(?<=dog)
...it's also checking the existence of "Cat":
(?!Cat)
...what I'm stuck on is how to essentially use a lookbehind on "Cat",
but only if it exists.
Hi Mike,

[Note: Please do a reply-to-all next time, so that everyone can help 
you.]

Regular expressions are a little evil at times; here's what I think 
you're
thinking of:

###
import re
pattern = re.compile(r"""dog(?!cat)
...                    | (?<=dogcat)""", re.VERBOSE)
pattern.match('dogman').start()
0
pattern.search('dogcatcher').start()
pattern.search('dogman').start()
0
pattern.search('catwoman')
###
but I can't be sure without seeing some of the examples you'd like the
regular expression to match against.
Best of wishes to you!
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