Allow attached parser to be a subclass of _SubparsersAction's parser class.

Author: kmvanbrunt

cmd2/argparse_custom.py

@@ -896,9 +896,9 @@ 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 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 TypeError: if subcommand_parser is not an instance of the following or their subclasses:
+                           1. Cmd2ArgumentParser
+                           2. 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):
@@ -910,12 +910,15 @@ def attach_subcommand(
         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:
+        # Verify the parser is compatible with the 'parser_class' configured for this
+        # subcommand group. We use isinstance() here to allow for subclasses, providing
+        # more flexibility than the standard add_parser() factory approach which enforces
+        # a specific class.
+        if not isinstance(subcommand_parser, subparsers_action._parser_class):
             raise TypeError(
-                f"The attached parser must be of type '{subparsers_action._parser_class.__name__}' "
-                f"to match the 'parser_class' configured for this subparsers action. "
-                f"Received '{type(subcommand_parser).__name__}'."
+                f"The attached parser must be an instance of '{subparsers_action._parser_class.__name__}' "
+                f"(or a subclass) to match the 'parser_class' configured for this subcommand group. "
+                f"Received: '{type(subcommand_parser).__name__}'."
             )
 
         # Use add_parser to register the subcommand name and any aliases

cmd2/cmd2.py

@@ -1189,9 +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 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 TypeError: if subcommand_parser is not an instance of the following or their subclasses:
+                           1. Cmd2ArgumentParser
+                           2. 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

@@ -430,19 +430,14 @@ def test_subcommand_attachment_errors() -> None:
     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="subclass")
-    with pytest.raises(TypeError, match="to match the 'parser_class' configured for this subparsers action"):
-        root_parser.attach_subcommand([], "sub", subclass_parser)
-
 
 def test_subcommand_attachment_parser_class_override() -> None:
     class MyParser(Cmd2ArgumentParser):
         pass
 
+    class MySubParser(MyParser):
+        pass
+
     root_parser = Cmd2ArgumentParser(prog="root")
 
     # Explicitly override parser_class for this subparsers action
@@ -452,9 +447,13 @@ class MyParser(Cmd2ArgumentParser):
     my_parser = MyParser(prog="sub")
     root_parser.attach_subcommand([], "sub", my_parser)
 
+    # Attaching a MySubParser instance should also succeed (isinstance check)
+    my_sub_parser = MySubParser(prog="sub2")
+    root_parser.attach_subcommand([], "sub2", my_sub_parser)
+
     # Attaching a standard Cmd2ArgumentParser instance should fail
     standard_parser = Cmd2ArgumentParser(prog="standard")
-    with pytest.raises(TypeError, match="The attached parser must be of type 'MyParser'"):
+    with pytest.raises(TypeError, match=r"must be an instance of 'MyParser' \(or a subclass\)"):
         root_parser.attach_subcommand([], "fail", standard_parser)