fix 3.8_08

mod_oop/3.8_08_stack.py

@@ -94,6 +94,22 @@ class Stack:
         else:
             self.bottom.next = obj
     
+    def pop(self) -> StackObj:
+        if not self.top:
+            return None
+
+        a, b, c = [self.top] + [None] * 2
+        while a:
+            a, b, c = a.next, a, b
+
+        if c:
+            c.next = None
+
+        if self.top in [b, c]:
+            self.top = None
+
+        return b
+
     def __len__(self):
         count, obj = 0, self.top
         while obj:
@@ -128,22 +144,6 @@ class Stack:
         else:
             self.top = value
 
-    def pop(self) -> StackObj:
-        if not self.top:
-            return None
-
-        a, b, c = [self.top] + [None] * 2
-        while a:
-            a, b, c = a.next, a, b
-
-        if c:
-            c.next = None
-
-        if self.top in [b, c]:
-            self.top = None
-
-        return b
-
     def get_data(self) -> List[StackObj]:
         return [x for x in self]
 
@@ -151,7 +151,7 @@ class Stack:
         return f"{self.__class__.__name__}({self.get_data()!r})"
 
     def __str__(self):
-        return " -> ".join(self.get_data())
+        return " -> ".join(map(str, self.get_data()))
 
 
 def tests():