[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!
>