Python vs. Perl, which is better to learn?

[Ian Bicking]

A few minor additions:

On Wed, 2002-05-01 at 08:58, Mark McEahern wrote:
> > A successful match sets a flurry of global variables:
> >
> >     $& = the matched portion of the input string
> >
> >     $` = everything before the match
> >
> >     $' = everything after the match
> 
> Thank Crom Python doesn't do that.  As someone else mentioned, these things
> are tucked away into match objects, if you want them, rather than being
> squirted into your namespace.

In particular, if you do:
match = someRegex.search(s)
match.group(0)    # Like $&
s[:match.start()] # Like #`
s[match.end():]   # Like #'
match.group(x)    # Like $x, where x is a number

Probably for any $ variable in Perl, there will be a fairly simple way
of getting the same result in Python.

> > Parentheses in the regex break the matching pattern into "groups" and the
> > portions of the string coresponding to each group may be accessed via:
> >
> >     $1, $2, ...
> >
> > E.g.,
> >
> >     s/^([^ ]* *([^ ]*)/$2 $1/;    # reverse order of 2 words
> 
> This switches the first and last words of a sentence.  I didn't bother
> putting the period back in there or sentence-casing the new first word.
> 
> import re
> s = "Explicit is better than implicit."
> pat = re.compile("^(\w+)(.* )(\w+)\.$")
> m = pat.search(s)
> if m:
>     print "%s%s%s" % (m.groups()[2], m.groups()[1], m.groups()[0])

Or you can do:

regex = re.compile(r'^([^ ]* *([^ ]*)')
transposed = regex.sub(lambda m: "%s %s" % (m.group(2), m.group(1)), s)

This is closer to the Perl example.  The lambda may leave it a bit
difficult to read, though :)  There must be something like
substitute-base-on-a-function in Perl, but it should be noted that while
it can be more awkward in some cases, it's also much more powerful than
the simple s/.../$2 $1/; substitution.  For instance, a very simple
templating system can be:

templateRE = re.compile(r'%%(.*?)%%')
def subTemplate(source, valueDict):
    return templateRE.sub(lambda m, valueDict=valueDict: valueDict.get(
                                 m.group(1), ''), source)


  Ian