On May 9, 5:00 am, Hrvoje Niksic <hnik...@xemacs.orgwrote:
I often have the need to match multiple regexes against a single
string, typically a line of input, like this:
if (matchobj = re1.match(line)):
... re1 matched; do something with matchobj ...
elif (matchobj = re2.match(line)):
... re2 matched; do something with matchobj ...
elif (matchobj = re3.match(line)):
....
Of course, that doesn't work as written because Python's assignments
are statements rather than expressions. The obvious rewrite results
in deeply nested if's:
matchobj = re1.match(line)
if matchobj:
... re1 matched; do something with matchobj ...
else:
matchobj = re2.match(line)
if matchobj:
... re2 matched; do something with matchobj ...
else:
matchobj = re3.match(line)
if matchobj:
...
Normally I have nothing against nested ifs, but in this case the deep
nesting unnecessarily complicates the code without providing
additional value -- the logic is still exactly equivalent to the
if/elif/elif/... shown above.
There are ways to work around the problem, for example by writing a
utility predicate that passes the match object as a side effect, but
that feels somewhat non-standard. I'd like to know if there is a
Python idiom that I'm missing. What would be the Pythonic way to
write the above code?
Hrvoje,
To make it more elegant I would do this:
1. Put all the ...do somethings... in functions like
re1_do_something(), re2_do_something(),...
2. Create a list of pairs of (re,func) in other words:
dispatch=[ (re1, re1_do_something), (re2, re2_do_something), ... ]
3. Then do:
for regex,func in dispatch:
if regex.match(line):
func(...)
Hope this helps,
-Nick Vatamaniuc
