Changed Stack.__str__ and fixed pop

Aufgabe03a.py

@@ -4,19 +4,14 @@ class Stack():
         self.stack = l
 
     def __str__(self):
-        result = ""
-        max_length = 1
-        if not self.isEmpty():
-            max_length = len(str(max(self.stack, key=lambda x: len(str(x)))))
-            vert = "\u2502"
-            for ele in reversed(self.stack):
-                result += vert + str(ele).rjust(max_length) + vert + "\n"
-        return result + "\u2514" + "\u2500"*max_length + "\u2518"
+        return str(self.stack)
 
     def push(self, element):
         self.stack.append(element)
 
     def pop(self):
+        if self.isEmpty():
+            raise ValueError("The Stack is empty!")
         element = self.stack[-1]
         del self.stack[-1]
         return element
@@ -65,6 +60,8 @@ class StackList:
         self.first_element = ListElement(value, self.first_element)
 
     def pop(self):
+        if self.isEmpty():
+            raise ValueError("The Stack is empty!")
         value = self.first_element.value
         self.first_element = self.first_element.next
         return value