A check has been added to know if args has an attribute 'callback'.

If args has no attribute callback, the help text should be printed. Because
there was a check to::
        if args.callback is 'x':
It would raise an error before the parser.print_help() was reached.

Author: JorisE

tmuxp/cli.py

@@ -965,7 +965,9 @@ def main():
     )
 
     try:
-        if args.callback is command_load:
+        if not hasattr(args, 'callback'):
+            parser.print_help()
+        elif args.callback is command_load:
             command_load(args)
         elif args.callback is command_convert:
             command_convert(args)
@@ -979,7 +981,5 @@ def main():
             command_attach_session(args)
         elif args.callback is command_kill_session:
             command_kill_session(args)
-        else:
-            parser.print_help()
     except KeyboardInterrupt:
         pass