[Tutor] regexp

[Steven D'Aprano]

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