Pascal's Triangle.py

class Solution(object):
    def generate(self, numRows):
        """
        :type numRows: int;; rtype: List[List[int]]
        """
        if not numRows: return []
        ret = [[1]]
        numRows -= 1
        while numRows:
            ret.append([1] + [a+b for a,b in zip(ret[-1][:-1], ret[-1][1:])] +[1])
            numRows-=1
        return ret