LeetCode - Pascal Triangle

Given numRows, generate the first numRows of Pascal's triangle.

For example, given numRows = 5,
Return

[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

Solution:

class Solution(object):
    def generate(self, numRows):
        lists = []
        for i in range(numRows):
            lists.append([1]*(i+1))
                if i>1 :
                    for j in range(1,i):
                        lists[i][j]=lists[i-1][j-1]+lists[i-1][j]
        return list
        """
        :type numRows: int
        :rtype: List[List[int]]
        """