Regex for Python 2.7

[Gabriel Genellina]

En Sat, 24 Jan 2009 21:51:31 -0200, MRAB <google at mrabarnett.plus.com>
escribió:

> Gabriel Genellina wrote:
>  > En Sat, 24 Jan 2009 18:23:51 -0200, MRAB <google at mrabarnett.plus.com>
>  > escribió:
>  >
>  >> Some time ago I discovered this difference between regular  
> expressions
>  >> in Python and Perl:
>  >>
>  >> Python
>  >>
>  >>     \A matches at start of string
>  >>     \Z matches at end of string
>  >>
>  >> Perl
>  >>
>  >>     \A matches at start of string
>  >>     \Z matches before terminal newline or at end of string
>  >>     \z matches at end of string
>  >>
>  >> In Perl \A == ^ and \Z == $ in single-string mode, but in Python \A  
> == ^
>  >> and \Z != $ in single-string mode.
>  >
>  > Why do you want the two to be equivalent? Isn't a good thing that you
>  > have both alternatives (\Z and $)? Use whichever is adequate in each  
> case.
>  >
> Python's \Z is equivalent to Perl's \z, but there's no equivalent to  
> Perl's \Z in multi-line mode.

I tested both:
<code>
import re

texts = ["abc\ndef", "abc\n", "abc"]
exprs = [
          re.compile(r"c$"),
          re.compile(r"c\Z"),
          re.compile(r"c$", re.MULTILINE),
          re.compile(r"c\Z", re.MULTILINE),
          ]
for text in texts:
          for expr in exprs:
            m = re.search(expr, text)
            print repr(text), expr.pattern, "match" if m else "no match"
</code>

c:\temp>python test_re.py
'abc\ndef' c$ no match
'abc\ndef' c\Z no match
'abc\ndef' c$ match
'abc\ndef' c\Z no match
'abc\n' c$ match
'abc\n' c\Z no match
'abc\n' c$ match
'abc\n' c\Z no match
'abc' c$ match
'abc' c\Z match
'abc' c$ match
'abc' c\Z match

<code>
@texts = ("abc\ndef", "abc\n", "abc");
@exprs = (qr/c$/,
                  qr/c\Z/,
                  qr/c$/m,
                  qr/c\Z/m,
#          qr/c\z/,
#          qr/c\z/m
                  );

foreach $text (@texts) {
          ($repr = $text) =~ s/\n/\\n/g;
          foreach $expr (@exprs) {
            print $repr, " ", $expr, " ";
            if ($text =~ $expr) {
              print "match\n";
            } else {
              print "no match\n";
            }
          }
}
</code>

c:\temp>perl test_re.pl
abc\ndef (?-xism:c$) no match
abc\ndef (?-xism:c\Z) no match
abc\ndef (?m-xis:c$) match
abc\ndef (?m-xis:c\Z) no match
abc\n (?-xism:c$) match
abc\n (?-xism:c\Z) match
abc\n (?m-xis:c$) match
abc\n (?m-xis:c\Z) match
abc (?-xism:c$) match
abc (?-xism:c\Z) match
abc (?m-xis:c$) match
abc (?m-xis:c\Z) match

If one wants to match end-of-line or end-of-string, use $ in multiline
mode. If one wants to match end-of-string only, use \Z. If one wants to
match end-of-line only, use \n [not shown].

-- 
Gabriel Genellina