match nested parenthesis

arn.zart at gmail.com arn.zart at gmail.com
Thu Jan 25 17:13:30 CET 2007


s99999999s2003 at yahoo.com wrote:
> hi
> i wish to find an reg exp for matching nested parenthesis of varying
> level like
> string =
> "somewords1(words(somewords2)-(some(some)words3)somestuff)somestuff"
> and be able to evaluate the pair starting from the inner most(the
> deepest level) , ie (some)
> up till the outer most. What is a good reg exp to do this? or is simple
> string manipulations enough?
> thanks

Evaluation using re.sub() and recursion (3 lines of code):

	def eval_sub(expr):
	  r"""Evaluate subexpressions in nested paired delimiters.

	  For example,
	  ‹  	single left-pointing angle quotation  	‹
	  › 	single right-pointing angle quotation 	›

	  >>> eval_sub('‹3 * ‹3 + ‹‹1 + 1› * 2›››')
	  '21'
	  >>> eval_sub('‹3 *  3 + ‹‹1 + 1› * 2›››') # test
mismatched delimiters
	  '13\x9b'
	  >>> '\x9b' == '›' # encoding ISO-8859-1
	  True
	  >>> eval_sub('3 * ‹‹1 + 1› * 2 + 3›') # test absence of
outer delimiters
	  '3 * 7'
	  """
	  val, n = re.subn("‹([^›‹]+)›", lambda m:
str(eval(m.group(1))), expr)
	  if n == 0:
	    return val
	  
	  return eval_sub(val)
	#end

This is just a proof of concept.




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