Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

[
  "((()))",
  "(()())",
  "(())()",
  "()(())",
  "()()()"
]

class Solution(object):
    def generateParenthesis(self, n, open=0):
        if n > 0 <= open:
            return ['(' + p for p in self.generateParenthesis(n-1, open+1)] + \
                   [')' + p for p in self.generateParenthesis(n, open-1)]
        return [')' * open] * (not n)