Kay Schluehr <[EMAIL PROTECTED]> wrote:
> I notice two issues here. Only one has anything to do with regular
> expressions. The other one with 'explicit is better than implicit': the
> many implicit passing operations of Rubys case statement. Using
> pseudo-Python notation this could be refactored into a more explicit
> and not far less concise style:
>
> if line.match( "title=(.*)" ) as m:
> print "Title is %s"%m.group(1)
> elif line.match( "track=(.*)" ) as m:
> print "Track is %s"%m.group(1)
> elif line.match( "artist=(.*)" ) as m:
> print "Artist is %s"%m.group(1)
>
> Here the result of the test line.match( ) is assigned to the local
> variable m if bool(line.match( )) == True. Later m can be used in the
> subsequent block.
Interesting!
This is exactly the area that (for me) python regexps' become more
clunky that perl's - not being able to assign and test the match
object in one line.
This leads to the rather wordy
m = re.match("title=(.*)", line)
if m:
print "Title is %s" % m.group(1)
else:
m = re.match("track=(.*)", line)
if m:
print "Track is %s"%m.group(1)
else:
m = re.match("artist=(.*)", line)
if m:
print "Artist is %s"%m.group(1)
If you could write
if re.match("title=(.*)", line) as m:
print "Title is %s" % m.group(1)
elif re.match("track=(.*)", line) as m:
print "Track is %s" % m.group(1)
elif re.match("artist=(.*)", line) as m:
print "Artist is %s" % m.group(1)
that would be a significant benefit.
You can of course define a helper class like this
class Matcher:
"""Regexp matcher helper"""
def match(self, r,s):
"""Do a regular expression match and return if it matched."""
self.value = re.match(r,s)
return self.value
def __getitem__(self, n):
"""Return n'th matched () item."""
return self.value.group(n)
Which makes this bit really quite neat
m = Matcher()
if m.match("title=(.*)", line):
print "Title is %s" % m[1]
elif m.match("track=(.*)", line):
print "Track is %s" % m[1]
elif m.match("artist=(.*)", line):
print "Artist is %s" % m[1]
> Moreover match becomes a string method. No need for extra importing
> re and applying re.compile(). Both can be done in str.match() if
> necessary.
I'm happy with the re module. Having transitioned from perl to python
some time ago now, I find myself using many fewer regexps due to the
much better built in string methods of python. This is a good thing,
because regexps should be used sparingly and they do degenerate into
line noise quite quickly...
--
Nick Craig-Wood <[EMAIL PROTECTED]> -- http://www.craig-wood.com/nick
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