129. Sum Root to Leaf Numbers

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

"""
integer,string, tuple are immutable, when passed in function they can not be modified in place 
immutable objects:
Numeric types: int, float, complex
string
tuple
frozen set
bytes
mutable:
list
dict
set
byte array
"""
class Solution(object):
    def sumNumbers(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if not root : return 0
        res=[]
        curr=[]
        def dfs(node,curr,res):
            curr.append(str(node.val))
            if not node.left and not node.right:
                #print curr
                res.append(int(''.join(curr)))
                
            else:
                if node.left:
                    dfs(node.left,curr,res)
                    curr.pop()
                if node.right:
                    dfs(node.right,curr,res)
                    curr.pop()
        dfs(root,curr,res)
        #print res
        return sum(res)