On Mon, 8 Mar 2010 16:12:35 +0000
Stephen Nelson-Smith <[email protected]> wrote:
> Hi,
>
> I've written this today:
>
> #!/usr/bin/env python
> import re
>
> pattern =
> r'(?P<ForwardedFor>^(-|[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}(,
> [0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3})*){1})
> (?P<RemoteLogname>(\S*)) (?P<RemoteUser>(\S*))
> (?P<Timestamp>(\[[^\]]+\]))
> (?P<FirstLineOfRequest>(\"([^"\\]*(?:\\.[^"\\]*)*)\")?)
> (?P<Status>(\S*)) (?P<Size>(\S*))
> (?P<Referrer>(\"([^"\\]*(?:\\.[^"\\]*)*)\")?)
> (?P<UserAgent>(\"([^"\\]*(?:\\.[^"\\]*)*)\")?)(
> )?(?P<SiteIntelligenceCookie>(\"([^"\\]*(?:\\.[^"\\]*)*)\")?)'
[...]
> It works fine, but it looks pretty unreadable and unmaintainable to
> anyone who hasn't spent all day writing regular expressions.
;-)
> I remember reading about verbose regular expressions. Would these help?
Yes, read the doc and tutorials about python regexes, you'll find some useful
features.
> How could I make the above more maintainable?
Maybe you can be interested in the following (seems to me it definitely fits
your case): I wrote a kind of "SuperPattern" ;-) extension that allows writing,
testing and composing sub-regexes.
I used {name} since this is illegal in a normal regex. Intended use was
something like:
import re ; Pattern = re.compile
person = Pattern(r"""...""")
email = Pattern(r"""...""")
phone = Pattern(r"""...""")
<when every subpattern works fine:>
entry = SuperPattern(scope, r"""{person}:\s+{email}\s*--\s*{phone}""")
<use entry>
Don't remember the details, but it was a very simple type to write (meta-using
re, indeed). The only point is that the constructor must be passed the scope
(typically locals(), else use globals() by default) where to find the
sub-patterns. Each regex pattern in fact has a .pattern attr (not sure of the
name) that actually holds its format string: so composing a superpattern is
just replacing a subpattern's name by its format.
> S.
>
Denis
--
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