How to make parentheses bold in a string?

In Python, I'm attempting to make a fast way of replacing bogus parentheses in a string with periods

• Let's say that I have a string with only '(', ')', and '.' and I want to replace all the () that don't match with corresponding () with a . For example: s1 = '((.))' s2 = '((.)' s3 = '(.))' Fixing these would give: rs1 = '((.))' rs2 = '.(.)' rs3 = '(.).' Right now, I'm using a stack to get all the bogus () then using a list comprehension to replace them. Given that fold is one of the s* strings above, here's my code: hashFoldStack = [] makePeriods = set() for hashFoldIndex, hashFoldCharacter in enumerate(fold): if hashFoldCharacter == '(': hashFoldStack.append(hashFoldIndex) elif hashFoldCharacter == ')': if len(hashFoldStack) > 0: hashFoldStack.pop() else: makePeriods.update([hashFoldIndex]) if len(hashFoldStack) > 0: for leftover in hashFoldStack: makePeriods.update(leftover) hashFold = ''.join(['.' if hashIndex in makePeriods\ else hashCharacter\ for hashIndex, hashCharacter\ in enumerate(fold)]) Question 1: For the first part where I'm creating the makePeriods stack, is there a faster way to do this? Question 2: Is a list comprehension going to be faster than a lambda or some function from the re module?

• Answer:

  I think the code is pretty fast. Let's make it work now :-) if len(hashFoldStack) > 0: for leftover in hashFoldStack: makePeriods.update(leftover) should be just: makePeriods.update(hashFoldStack) I was searching net a bit and http://www.skymind.com/~ocrow/python_string/ I found a great article about the topic. It mentions that the string construction by join and list comprehension is one of the fastest ways. If you want to optimize further, use some way of profiling as the comments suggest. You can wrap the code in for loop that runs lots of times and then launch the script like this $ python -m cProfile script.py. By the way, there could be a way to make it faster by constructing hashFoldList in the loop together with hashFoldStack. At the end, it would be just: hashFold = ''.join(hashFoldList). Anyway, an interesting question.