Leetcode: Populating Next Right Pointers in Each Node II @Python

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

class Solution:
    # @param root, a tree node
    # @return nothing
    def connect(self, root):
        crt=root
        while crt:
            firstNextLevel=None
            prev=None
            while crt:
                if not firstNextLevel:
                    firstNextLevel=crt.left if crt.left else crt.right
                if crt.left:
                    if prev:
                        prev.next=crt.left
                    prev=crt.left
                if crt.right:
                    if prev:
                        prev.next=crt.right
                    prev=crt.right
                crt=crt.next
            crt=firstNextLevel