improvement: list available commands for cli

spotify2ytmusic/__main__.py

@@ -2,16 +2,26 @@
 
 from . import cli
 import sys
+import inspect
+
+def list_commands(module):
+    # include only functions defined in e.g. 'cli' module
+    commands = [name for name, obj in inspect.getmembers(module) if inspect.isfunction(obj)]
+    return commands
+
+available_commands = list_commands(cli)
 
 if len(sys.argv) < 2:
     print(f"usage: spotify2ytmusic [COMMAND] <ARGUMENTS>")
-    print("       For example, try 'list_playlists'")
+    print("Available commands:", ", ".join(available_commands))
+    print("       For example, try 'spotify2ytmusic list_playlists'")
     sys.exit(1)
 
-if not hasattr(cli, sys.argv[1]):
+if sys.argv[1] not in available_commands:
     print(
-        f"ERROR: Unknown command, see https://github.com/linsomniac/spotify_to_ytmusic"
+        f"ERROR: Unknown command '{sys.argv[1]}', see https://github.com/linsomniac/spotify_to_ytmusic"
     )
+    print("Available commands: ", ", ".join(available_commands))
     sys.exit(1)
 
 fn = getattr(cli, sys.argv[1])