Cmds / Cmd: Add comments and debug logging

Add some comments and a little debug logging to clarify operation.

Signed-off-by: Jan Lindemann <jan@janware.com>

tools/python/jwutils/Cmd.py

@@ -49,5 +49,7 @@ class Cmd(ABC): # export
             return
         self.child_classes.append(cmd)
 
+    # To be overriden by derived class in case the command does take arguments.
+    # Will be called from App base class constructor and set up the parser hierarchy
     def add_arguments(self, parser: ArgumentParser) -> None:
         pass

tools/python/jwutils/Cmds.py

@@ -15,7 +15,11 @@ from jwutils.log import *
 class Cmds: # export
 
     def __instantiate(self, cls):
+        try:
             r = cls()
+        except Exception as e:
+            slog(ERR, f'Failed to instantiate command of type {cls}: {e}')
+            raise
         r.cmds = self # TODO: Rename Cmds class to App, "Cmds" isn't very self-explanatory
         r.app = self
         return r
@@ -86,6 +90,7 @@ class Cmds: # export
         cmds = [cmd for cmd in self.__cmds if type(cmd) not in subcmds]
         subparsers = self.__parser.add_subparsers(title='Available commands', metavar='')
         for cmd in cmds:
+            slog(DEBUG, f'Adding top-level command {cmd} to parser')
             self.__add_cmd_to_parser(cmd, subparsers)
 
     async def __run(self, argv=None):