Steven D'Aprano wrote:
> Oh, a further thought...
>
>
> On Thursday 05 May 2016 16:46, Stephen Hansen wrote:
>
>> On Wed, May 4, 2016, at 11:04 PM, Steven D'Aprano wrote:
>>> Start by writing a function or a regex that will distinguish strings
>>> that match your conditions from those that don't. A regex might be
>>> faster, but here's a function version.
>>> ... snip ...
>>
>> Yikes. I'm all for the idea that one shouldn't go to regex when Python's
>> powerful string type can answer the problem more clearly, but this seems
>> to go out of its way to do otherwise.
>>
>> I don't even care about faster: Its overly complicated. Sometimes a
>> regular expression really is the clearest way to solve a problem.
>
> Putting non-ASCII letters aside for the moment, how would you match these
> specs as a regular expression?
>
> - All uppercase ASCII letters (A to Z only), optionally separated into
> words by either a bare ampersand (e.g. "AAA&AAA") or an ampersand with
> leading and
> trailing spaces (spaces only, not arbitrary whitespace): "AAA & AAA".
>
> - The number of spaces on either side of the ampersands need not be the
> same: "AAA& BBB & CCC" should match.
>
> - Leading or trailing spaces, or spaces not surrounding an ampersand, must
> not match: "AAA BBB" must be rejected.
>
> - Leading or trailing ampersands must also be rejected. This includes the
> case where the string is nothing but ampersands.
>
> - Consecutive ampersands "AAA&&&BBB" and the empty string must be
> rejected.
>
>
> I get something like this:
>
> r"(^[A-Z]+$)|(^([A-Z]+[ ]*\&[ ]*[A-Z]+)+$)"
>
>
> but it fails on strings like "AA & A & A". What am I doing wrong?
>
>
> For the record, here's my brief test suite:
>
>
> def test(pat):
> for s in ("", " ", "&" "A A", "A&", "&A", "A&&A", "A& &A"):
> assert re.match(pat, s) is None
> for s in ("A", "A & A", "AA&A", "AA & A & A"):
> assert re.match(pat, s)
>>> def test(pat):
... for s in ("", " ", "&" "A A", "A&", "&A", "A&&A", "A& &A"):
... assert re.match(pat, s) is None
... for s in ("A", "A & A", "AA&A", "AA & A & A"):
... assert re.match(pat, s)
...
>>> test("^A+( *& *A+)*$")
>>>
--
https://mail.python.org/mailman/listinfo/python-list
