Changed __str__

Aufgabe03a.py

@@ -3,7 +3,12 @@ class Stack(list):
         self.stack = l
     
     def __str__(self):
-        return str(self.stack)
+        max_length = len(str(max(self.stack, key=lambda x: len(str(x)))))
+        result = ""
+        vert = "\u2502"
+        for ele in self.stack:
+            result += vert + str(ele).rjust(max_length) + vert + "\n"
+        return result + "\u2514" + "\u2500"*max_length + "\u2518"
 
     def push(self, element):
         self.stack.append(element)