need some regular expression help

John Machin sjmachin at
Sun Oct 8 00:06:28 CEST 2006

Chris wrote:
> I need a pattern that  matches a string that has the same number of '('
> as ')':
> findall( compile('...'), '42^((2x+2)sin(x)) + (log(2)/log(5))' ) = [
> '((2x+2)sin(x))', '(log(2)/log(5))' ]
> Can anybody help me out?

No, there is so such pattern. You will have to code up a function.

Consider what your spec really is: '42^((2x+2)sin(x)) +
(log(2)/log(5))' has the same number of left and right parentheses; so
does the zero-length string; so does ') + (' -- perhaps you need to add
'and starts with a "("'

Consider what you are going to do with input like this:

    print '(' + some_text + ')'

Maybe you need to do some lexical analysis and work at the level of
tokens rather than individual characters.

Which then raises the usual question: you have a perception that
regular expressions are the solution -- to what problem??


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