[Python-ideas] Adding function checks to regex
python at mrabarnett.plus.com
Sat Mar 19 04:25:57 CET 2011
Some of those who are relative new to regexes sometimes ask how to write
a regex which checks that a number is in a range or is a valid date.
Although this may be possible, it certainly isn't easy.
From what I've read, Perl has a way of including code in a regex, but I
don't think that's a good idea
However, it occurs to me that there may be a case for being able to call
a supplied function to perform such checking.
Borrowing some syntax from Perl, it could look like this:
return 1 <= int(m.group()) <= 10
numbers = regex.findall(r"\b\d+\b(*CALL)", text, call=range_check)
The regex module would match as normal until the "(*CALL)", at which
point it would call the function. If the function returns True, the
matching continues (and succeeds); if the function returns False, the
matching backtracks (and fails).
The function would be passed a match object.
An extension, again borrowing the syntax from Perl, could include a tag
numbers = regex.findall(r"\b\d+\b(*CALL:RANGE)", text,
The tag would be passed to the function so that it could support
Alternatively, a tag could always be passed; if no tag is provided then
None would be passed instead.
There's also the additional possibility of providing a dict of functions
instead and using the tag to select the function which should be called.
I'd be interested in your opinions.
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