re Challenge: More Compact?

[Moshe Zadka]

On Mon, 16 Jul 2001 00:58:46 GMT, tim at vegeta.ath.cx (Tim Hammerquist) wrote:

> Easily implemented in Perl:
> 
> : sub valid_ip {
> :     my ($ip, $failed, @elements) = (shift, 0);
> :     @elements = ($ip =~ /^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$/);
> :     $failed = grep { $_ > 255 } @elements;
> :     return ($failed) ? undef : 1;
> : }
> 
> Slightly more verbose in Python:
> 
> : import re
> : def valid_ip(ip):
> :     expr = r'^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$'
> :     elements = map(int, re.match(expr, ip).groups())
> :     failed = filter(lambda x: x > 255, elements)
> :     if failed:  return None
> :     else:       return 1

In the interest of "fair" Python/Perl comparisons:

: import re
: def valid_ip(ip):
:     expr = r'^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$'
:     elements = map(int, re.match(expr, ip).groups())
:     failed = filter(lambda x: x > 255, elements)
:     return !failed

Exactly the same as the Perl version.

the "import re" line is offset by Python doing parameter passing
itself, and all the rest correspond line-for-line.
Of course, using list-comps, it might be easier:

: import re
: def valid_ip(ip):
:     expr = r'^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$'
:     failed = [x if int(x)>255 for x in re.match(expr, ip).groups()]
:     return !failed

Of course, I would never write that way -- here's more idiomatic Python:

: import re
: valid_ip_re = re.compile(r'^(\d{1,3})\.(\d{1,3})\.(\d{1,3})\.(\d{1,3})$')
: def valid_ip(ip):
:    match = valid_ip_re.match(ip)
:    if not match:
:        return
:    return ![x if int(x)>255 for x in match.groups()]
  
And now it's even correct!
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