[Tutor] regexp

[Dinara Vakhitova]

Sorry, I didn´t know that I couldn´t ask questions about the homework...
I wanted to do it recursively, like this:

def check_abc(string):
    string = string.lower()
    check_pair = re.compile("([a-z])[\1-z]")
    if check_pair.match(string):
        if check_abc(string[1:]):
            return True
        else:
            return False
    else:
        return False

the only problem is that this regex doesn´t work and this case is not
specified in the Python documentation...

Excuse me for disturbing you.

2011/11/5 Steven D'Aprano <steve at pearwood.info>

> Dinara Vakhitova wrote:
>
>> Thank you for your answer, Steven.
>>
>> Of course it would have been easier to write this function,
>> but unfortunately my task is to do it with a regular expression :(
>>
>
> Is this homework? You should have said so.
>
> I don't understand questions like this. Do carpenters ask their
> apprentices to cut a piece of wood with a hammer? Do apprentice chefs get
> told to dice carrots using only a spoon? Computer programming is the only
> skill I know of where teachers routinely insist that students use
> inappropriate tools to solve a problem, just to prove they can do it.
>
> In any case, if this is even possible using regular expressions -- and I
> don't think it is -- I have no idea how to do it. Good luck. Maybe somebody
> else might have a clue.
>
> I don't think it's possible because you don't know how many characters the
> string will have. Even if [\1-z] works (which it doesn't), you still have
> the same problem that you don't know where to stop:
>
> [a-z][\1-z][\2-z][\3-z][\4-z].**..[\99-z]
>
> This is related to the reason you can't parse indefinitely nested
> parentheses using a regular expression.
>
>
>
>
> --
> Steven
>
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-- 
*Yours faithfully,
Dinara Vakhitova*
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