[EMAIL PROTECTED] wrote:
> Hi,
>
> I'd need to perform simple pattern matching within a string using a
> list of possible patterns. For example, I want to know if the substring
> starting at position n matches any of the string I have a list, as
> below:
>
> sentence = "the color is $red"
> patterns = ["blue","red","yellow"]
> pos = sentence.find($)
> # here I need to find whether what's after 'pos' matches any of the
> strings of my 'patterns' list
> bmatch = ismatching( sentence[pos:], patterns)
>
> Is an equivalent of this ismatching() function existing in some Python
> lib?
>
> Thanks,
>
> Olivier.
>
As I think you define it, ismatching can be written as:
>>> def ismatching(sentence, patterns):
... re_pattern = re.compile("(%s)\Z" % "|".join(patterns))
... return bool(re_pattern.match(sentence))
...
>>> ismatching(sentence[pos+1:], patterns)
True
>>> ismatching(sentence[pos+1:], ["green", "blue"])
False
>>>
(For help with regular expressions, see: http://www.amk.ca/python/howto/regex/)
or, you can ask the regexp engine to starting looking at a point you specify:
>>> def ismatching(sentence, patterns, startingpos = 0):
... re_pattern = re.compile("(%s)\Z" % "|".join(patterns))
... return bool(re_pattern.match(sentence, startingpos))
...
>>> ismatching(sentence, patterns, pos+1)
True
>>>
but, you may be able to save the separate step of determining pos, by including
it in the regexp, e.g.,
>>> def matching(patterns, sentence):
... re_pattern = re.compile("\$(%s)" % "|".join(patterns))
... return bool(re_pattern.search(sentence))
...
>>> matching(patterns, sentence)
True
>>> matching(["green", "blue"], sentence)
False
>>>
then, it might be more general useful to return the match, rather than the
boolean value - you can still use it in truth testing, since a no-match will
evaluate to False
>>> def matching(patterns, sentence):
... re_pattern = re.compile("\$(%s)" % "|".join(patterns))
... return re_pattern.search(sentence)
...
>>> if matching(patterns, sentence): print "Match"
...
Match
>>>
Finally, if you are going to be doing a lot of these it would be faster to take
the pattern compilation out of the function, and simply use the pre-compiled
regexp, or as below, its bound method: search:
>>> matching = re.compile("\$(%s)\Z" % "|".join(patterns)).search
>>> matching(sentence)
<_sre.SRE_Match object at 0x01847E60>
>>> bool(_)
True
>>> bool(matching("the color is $red but there is more"))
False
>>> bool(matching("the color is $pink"))
False
>>> bool(matching("the $color is $red"))
True
>>>
HTH
Michael
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