On Thu, Mar 28, 2013 at 9:00 PM, Victor Hooi <victorh...@gmail.com> wrote:
> Hi,
>
> I have logline that I need to test against multiple regexes. E.g.:
>
> import re
>
> expression1 = re.compile(r'....')
> expression2 = re.compile(r'....')
>
> with open('log.txt') as f:
> for line in f:
> if expression1.match(line):
> # Do something - extract fields from line.
> elif expression2.match(line):
> # Do something else - extract fields from line.
> else:
> # Oh noes! Raise exception.
>
> However, in the "Do something" section - I need access to the match object
> itself, so that I can strip out certain fields from the line.
>
> Is it possible to somehow test for a match, as well as do assignment of the
> re match object to a variable?
>
> if expression1.match(line) = results:
> results.groupsdict()...
AFAIK, not without hacks and/or being unidiomatic.
> Obviously the above won't work - however, is there a Pythonic way to tackle
> this?
>
> What I'm trying to avoid is this:
>
> if expression1.match(line):
> results = expression1.match(line)
>
> which I assume would call the regex match against the line twice - and when
> I'm dealing with a huge amount of log lines, slow things down.
def process(line):
match = expr1.match(line)
if match:
# ...extract fields…
return something
match = expr2.match(line)
if match:
# ...extract fields…
return something
# etc…
raise SomeError() # Oh noes!
with open('log.txt') as f:
for line in f:
results = process(line)
If you choose to further move the extractor snippets into their own
functions, then you can do:
# these could be lambdas if they're simple enough
def case1(match):
# ...
def case2(match):
# …
# etc...
REGEX_EXTRACTOR_PAIRS = [
(re.compile(r'....'), case1),
(re.compile(r'....'), case2),
# etc...
]
def process(line):
for regex, extractor in REGEX_EXTRACTOR_PAIRS:
match = regex.match(line)
if match:
return extractor(match)
raise SomeError()
Although this second option is likely somewhat less performant, but it
definitely saves on repetition.
Cheers,
Chris
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