new_contents: # Definition for a binary tree node.
  # class TreeNode(object):
  #     def __init__(self, x):
  #         self.val = x
  #         self.left = None
  #         self.right = None
  
  class Solution(object):
      def sumOfLeftLeaves(self, root):
          """
          :type root: TreeNode
          :rtype: int
          """
          ans = 0
          if root:
              if root.left:
                  if root.left.left is None and root.left.right is None:
                      ans += root.left.val
                  else:
                      ans += self.sumOfLeftLeaves(root.left)
              ans += self.sumOfLeftLeaves(root.right)
          return ans
  
subject: Add py solution for 404. Sum of Left Leaves