Add typing annotations to Python codes. (#411)

codes/python/chapter_tree/binary_tree_bfs.py

@@ -9,20 +9,20 @@ sys.path.append(osp.dirname(osp.dirname(osp.abspath(__file__))))
 from modules import *
 
 
-def level_order(root: Optional[TreeNode]):
+def level_order(root: Optional[TreeNode]) -> List[int]:
     """ 层序遍历 """
     # 初始化队列，加入根结点
-    queue = collections.deque()
+    queue: Deque[TreeNode] = collections.deque()
     queue.append(root)
     # 初始化一个列表，用于保存遍历序列
-    res = []
+    res: List[int] = []
     while queue:
-        node = queue.popleft()       # 队列出队
-        res.append(node.val)         # 保存结点值
+        node: TreeNode = queue.popleft() # 队列出队
+        res.append(node.val)             # 保存结点值
         if node.left is not None:
-            queue.append(node.left)  # 左子结点入队
+            queue.append(node.left)      # 左子结点入队
         if node.right is not None:
-            queue.append(node.right) # 右子结点入队
+            queue.append(node.right)     # 右子结点入队
     return res
 
 
@@ -30,11 +30,11 @@ def level_order(root: Optional[TreeNode]):
 if __name__ == "__main__":
     # 初始化二叉树
     # 这里借助了一个从数组直接生成二叉树的函数
-    root = list_to_tree(arr=[1, 2, 3, 4, 5, 6, 7])
+    root: TreeNode = list_to_tree(arr=[1, 2, 3, 4, 5, 6, 7])
     print("\n初始化二叉树\n")
     print_tree(root)
 
     # 层序遍历
-    res = level_order(root)
+    res: List[int] = level_order(root)
     print("\n层序遍历的结点打印序列 = ", res)
     assert res == [1, 2, 3, 4, 5, 6, 7]