Confirm attached parser is a Cmd2ArgumentParser-derived class.

Author: kmvanbrunt

cmd2/argparse_custom.py

@@ -896,13 +896,21 @@ def attach_subcommand(
         :param subcommand: name of the new subcommand
         :param subcommand_parser: the parser to attach
         :param add_parser_kwargs: additional arguments for the subparser registration (e.g. help, aliases)
-        :raises TypeError: if the subcommand parser's type does not match the 'parser_class' configured
-                           for the target subcommand group.
+        :raises TypeError: if the subcommand parser is not an instance of 'Cmd2ArgumentParser'
+                           (or one of its subclasses), or if its type does not match the 'parser_class'
+                           configured for the target subcommand group.
         :raises ValueError: if the command path is invalid or doesn't support subcommands
         """
+        if not isinstance(subcommand_parser, Cmd2ArgumentParser):
+            raise TypeError(
+                f"The attached parser must be an instance of 'Cmd2ArgumentParser' (or a subclass). "
+                f"Received: '{type(subcommand_parser).__name__}'."
+            )
+
         target_parser = self._find_parser(subcommand_path)
         subparsers_action = target_parser._get_subparsers_action()
 
+        # Mirror argparse's add_parser() behavior by requiring an exact type match with _parser_class
         if type(subcommand_parser) is not subparsers_action._parser_class:
             raise TypeError(
                 f"The attached parser must be of type '{subparsers_action._parser_class.__name__}' "

cmd2/cmd2.py

@@ -1189,8 +1189,9 @@ def attach_subcommand(
         :param subcommand: name of the new subcommand
         :param subcommand_parser: the parser to attach
         :param add_parser_kwargs: additional arguments for the subparser registration (e.g. help, aliases)
-        :raises TypeError: if the subcommand parser's type does not match the 'parser_class' configured
-                           for the target subcommand group.
+        :raises TypeError: if the subcommand parser is not an instance of 'Cmd2ArgumentParser'
+                           (or one of its subclasses), or if its type does not match the 'parser_class'
+                           configured for the target subcommand group.
         :raises ValueError: if the command path is invalid or doesn't support subcommands
         """
         root_parser, subcommand_path = self._get_root_parser_and_subcmd_path(command)

tests/test_argparse_custom.py

@@ -425,12 +425,17 @@ def test_subcommand_attachment_errors() -> None:
     with pytest.raises(ValueError, match="Subcommand 'fake' not found in 'root'"):
         root_parser.detach_subcommand([], "fake")
 
+    # Verify TypeError when attaching a non-Cmd2ArgumentParser type
+    ap_parser = argparse.ArgumentParser(prog="non-cmd2-parser")
+    with pytest.raises(TypeError, match=r"must be an instance of 'Cmd2ArgumentParser' \(or a subclass\)"):
+        root_parser.attach_subcommand([], "sub", ap_parser)  # type: ignore[arg-type]
+
     # Verify TypeError when attaching a parser of a different type
     class SubParser(Cmd2ArgumentParser):
         pass
 
-    subclass_parser = SubParser(prog="sub")
-    with pytest.raises(TypeError, match="The attached parser must be of type 'Cmd2ArgumentParser'"):
+    subclass_parser = SubParser(prog="subclass")
+    with pytest.raises(TypeError, match="to match the 'parser_class' configured for this subparsers action"):
         root_parser.attach_subcommand([], "sub", subclass_parser)
 
 

tests/test_cmd2.py

@@ -4534,9 +4534,3 @@ def do_no_argparse(self, _statement: cmd2.Statement) -> None:
     # Test command that doesn't use argparse
     with pytest.raises(ValueError, match="Command 'no_argparse' does not use argparse"):
         app.attach_subcommand("no_argparse", "sub", cmd2.Cmd2ArgumentParser())
-
-    # Test type mismatch
-    import argparse
-
-    with pytest.raises(TypeError, match="to match the 'parser_class' configured for this subparsers action"):
-        app.attach_subcommand("alias", "sub", argparse.ArgumentParser())  # type: ignore[arg-type]