Add typing annotations to Python codes. (#411)

codes/python/chapter_stack_and_queue/stack.py

@@ -13,7 +13,7 @@ from modules import *
 if __name__ == "__main__":
     """ 初始化栈 """
     # Python 没有内置的栈类，可以把 list 当作栈来使用 
-    stack = []
+    stack: List[int] = []
 
     """ 元素入栈 """
     stack.append(1)
@@ -24,18 +24,18 @@ if __name__ == "__main__":
     print("栈 stack =", stack)
 
     """ 访问栈顶元素 """
-    peek = stack[-1]
+    peek: int = stack[-1]
     print("栈顶元素 peek =", peek)
 
     """ 元素出栈 """
-    pop = stack.pop()
+    pop: int = stack.pop()
     print("出栈元素 pop =", pop)
     print("出栈后 stack =", stack)
 
     """ 获取栈的长度 """
-    size = len(stack)
+    size: int = len(stack)
     print("栈的长度 size =", size)
 
     """ 判断是否为空 """
-    is_empty = len(stack) == 0
+    is_empty: bool = len(stack) == 0
     print("栈是否为空 =", is_empty)