On 22 Dec 2004 17:30:04 GMT, Nick Craig-Wood <[EMAIL PROTECTED]> wrote:
> Is there an easy way round this? AFAIK you can't assign a variable in
> a compound statement, so you can't use elif at all here and hence the
> problem?
>
> I suppose you could use a monstrosity like this, which relies on the
> fact that list.append() returns None...
>
> line = "123123"
> m = []
> if m.append(re.search(r'^(\d+)$', line)) or m[-1]:
> print "int",int(m[-1].group(1))
> elif m.append(re.search(r'^(\d*\.\d*)$', line)) or m[-1]:
> print "float",float(m[-1].group(1))
> else:
> print "unknown thing", line
I wrote a scanner for a recursive decent parser a while back. This is
the pattern i used for using mulitple regexps, instead of using an
if/elif/else chain.
import re
patterns = [
(re.compile('^(\d+)$'),int),
(re.compile('^(\d+\.\d*)$'),float),
]
def convert(s):
for regexp, action in patterns:
m = regexp.match(s)
if not m:
continue
return action(m.group(1))
raise ValueError, "Invalid input %r, was not a numeric string" % (s,)
if __name__ == '__main__':
tests = [ ("123123",123123), ("123.123",123.123), ("123.",123.) ]
for input, expected in tests:
assert convert(input) == expected
try:
convert('')
convert('abc')
except:
pass
else:
assert None,"Should Raise on invalid input"
Of course, I wrote the tests first. I used your regexp's but I was
confused as to why you were always using .group(1), but decided to
leave it. I would probably actually send the entire match object to
the action. Using something like:
(re.compile('^(\d+)$'),lambda m:int(m.group(1)),
and
return action(m)
but lambdas are going out fashion. :(
Stephen Thorne
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