newly created test server works so why the fuck does my other server not work

testserverwithclass.py

@@ -17,15 +17,15 @@ class MyClass():
 
         connected = True
         while connected:
-            msg_length = conn.recv(HEADER).decode(FORMAT)
+            msg_length = conn.recv(self.HEADER).decode(self.FORMAT)
             if msg_length:
                 msg_length = int(msg_length)
-                msg = conn.recv(msg_length).decode(FORMAT)
-                if msg == DISCONNECT_MESSAGE:
+                msg = conn.recv(msg_length).decode(self.FORMAT)
+                if msg == self.DISCONNECT_MESSAGE:
                     connected = False
 
                 print(f"[{addr}] {msg}")
-                conn.send("Msg received".encode(FORMAT))
+                conn.send("Msg received".encode(self.FORMAT))
         conn.close()