Is it bug or feature in sre?

Skip Montanaro skip at pobox.com
Mon Jan 5 13:07:13 CET 2004


    >>> re.compile("(?P<gr>[A-Z]*)?")
    Roman> Traceback (most recent call last):
    ...
    Roman> sre_constants.error: nothing to repeat

    Roman> I wonder why I can't do this?

Is there some reason why

    "(?P<gr>[A-Z]*)"

or

    "(?P<gr>[A-Z]+)?"

isn't sufficient?  You specified the zero-or-more repetition inside the
group.  There's nothing else to have zero-or-one of.


    Roman> I guess it's of terrible style, but is this behaviour intentional
    Roman> or not?

I suspect it's intentional, since Fredrik went to the trouble of raising an
exception with a useful error message. <wink>

    Roman> Probably it is good idea to mention this in Python update path
    Roman> documents.  Otherwise some old programs will mysteriously fail.

What were you converting from, an older version of sre, pre, regex, or
(shudder) regexp?

Skip




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