Implemented check_klammern

Aufgabe03b.py

+from Aufgabe03a import Stack
+
+def end(c):
+    if c == "(": return ")"
+    if c == "[": return "]"
+    if c == "<": return ">"
+    if c == "{": return "}"
+    return None
+
+def check_klammern(s):
+    check_sum = Stack()
+    for c in s:
+        if c in ["(", "[", "<", "{"]:
+            check_sum.push(c)
+        elif c in [")", "]", ">", "}"]:
+            if check_sum.isEmpty():
+                return False
+            elif c == end(check_sum.pop()):
+                continue
+            else:
+                return False
+    return check_sum.isEmpty()