re question - finiding matching ()

[Jeff Epler]

Regular Expressions cannot perform the simple task of matching an
arbitrary number of parentheses.  You could write an expression that
will work as long as the nesting isn't more than N levels, but the
expression quickly becomes very painful.

Instead, you can use some method to split the string into parts: one
part for "(", one for ")" and one for any other sequence of characters:

tokenize_re = re.compile("\(|\)|[^()]*")

Now, use this expression to tokenize your input string:

>>> tokens = tokenize_re.findall("add((2 * 2), 100)")
>>> print tokens
['add', '(', '(', '2 * 2', ')', ', 100', ')']
To match your language, the first token must be 'add':
	if tokens[0] != 'add': # no match
The second token must be '(':
	if tokens[1] != '(': # no match
Now, start scanning and counting parens, until you get back to 0
	nesting_level = 0
	for t in tokens[1:]:
		if t == ')':
			nesting_level -= 1
			if nesting_level == 0:
				# End of desired string
		else if t == '(':
			nesting_level += 1
	# if you end the loop without reaching nesting_level 0
	# then there were not enough close-parens
	# no match
You could also implement this part recursively (as you likely would if
you were actually compiling the string into bytecode).

Jeff