From c1811ded3f634be827aef68623f72d823b175a28 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=ED=95=9C=EB=B0=94=EB=A6=84?=
 <48576227+rumbarum@users.noreply.github.com>
Date: Mon, 15 Aug 2022 18:36:56 +0900
Subject: [PATCH] fix method pop for stack
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pyright version 1.1.266, mypy 0.971 에서 Type Check시 에러가 발생하네요

pyright error
-  error: "item" is not a known member of "None" (reportOptionalMemberAccess)
-  error: "pointer" is not a known member of "None" (reportOptionalMemberAccess)
- error: Function with declared type of "T@Stack" must return value
    Type "None" cannot be assigned to type "T@Stack" (reportGeneralTypeIssues)

mypy error
- error: Item "None" of "Optional[Node[Any]]" has no attribute "item"

해당 에러들 안나는 방향으로 수정 했습니다.
수정 해보니 pyright랑 mypy 랑 잡는 부분이 다르긴 하네요.
---
 .../03-linked-list.py"                         | 18 ++++++++++--------
 1 file changed, 10 insertions(+), 8 deletions(-)

diff --git "a/03 \353\263\264\353\204\210\354\212\244 - \353\260\260\354\232\264 \352\262\203 \354\235\221\354\232\251\355\225\230\352\270\260/03-linked-list.py" "b/03 \353\263\264\353\204\210\354\212\244 - \353\260\260\354\232\264 \352\262\203 \354\235\221\354\232\251\355\225\230\352\270\260/03-linked-list.py"
index 4d928f7..1fefd76 100644
--- "a/03 \353\263\264\353\204\210\354\212\244 - \353\260\260\354\232\264 \352\262\203 \354\235\221\354\232\251\355\225\230\352\270\260/03-linked-list.py"	
+++ "b/03 \353\263\264\353\204\210\354\212\244 - \353\260\260\354\232\264 \352\262\203 \354\235\221\354\232\251\355\225\230\352\270\260/03-linked-list.py"	
@@ -47,18 +47,20 @@ def push(self, item: T) -> None:
             cur_node = cur_node.pointer
         cur_node.pointer = new_node
 
-    def pop(self) -> T:
+    def pop(self) -> Optional[T]:
         if self.head is None:
-            raise ValueError("stack is empty")
-        cur_node = self.head
+            raise ValueError("Stack is empty")
+        cur_node: Node[T] = self.head
         if cur_node.pointer is None:
             self.head = None
             return cur_node.item
-        while cur_node.pointer.pointer is not None:
-            cur_node = cur_node.pointer
-        result = cur_node.pointer
-        cur_node.pointer = None
-        return result.item
+        while cur_node.pointer is not None:
+            if cur_node.pointer.pointer is not None:
+                cur_node = cur_node.pointer
+                continue
+            result = cur_node.pointer
+            cur_node.pointer = None
+            return result.item if result is not None else None
 
 
 class Queue(Generic[T], LinkedList[T]):