Pascal's Triangle

Given a non-negative integer numRows, generate the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it.

Example:

Input: 5
Output:
[
     [1],
    [1,1],
   [1,2,1],
  [1,3,3,1],
 [1,4,6,4,1]
]

My solution:

class Solution:
    def generate(self, numRows):
        """
        :type numRows: int
        :rtype: List[List[int]]
        """
        result = list()

        if numRows > 0:
            result.append([1])
        else:
            return result

        for j in range(numRows - 1):
            tmp = list()
            index = len(result) - 1
            for i in range(j + 2):
                if i == 0:
                    tmp.append(result[index][i])
                    continue

                if i == len(result):
                    tmp.append(result[index][i - 1])
                    break

                add = result[index][i - 1] + result[index][i]
                tmp.append(add)

            result.append(tmp)

        return result