Remove dependency on Python's built-in cmd module (#1539)

* Remove dependency on Python's built-in cmd module

The cmd2.Cmd class no longer inhertis from cmd.Cmd

* Address PR comments

* Add missing unit test for custom stdout

* Deleted an unused method and updated a method comment

* Updated command completion tests to use complete_tester().

---------

Co-authored-by: Kevin Van Brunt <kmvanbrunt@gmail.com>

Author: tleonhardt

CHANGELOG.md

@@ -1,3 +1,9 @@
+## 4.0.0 (TBD, 2026)
+
+- Potentially Breaking Changes
+    - `cmd2` no longer has a dependency on `cmd` and `cmd2.Cmd` no longer inherits from `cmd.Cmd`
+        - We don't _think_ this should impact users, but there is theoretically a possibility
+
 ## 3.0.0 (December 7, 2025)
 
 ### Summary

cmd2/cmd2.py

@@ -1,32 +1,33 @@
-"""Variant on standard library's cmd with extra features.
-
-To use, simply import cmd2.Cmd instead of cmd.Cmd; use precisely as though you
-were using the standard library's cmd, while enjoying the extra features.
-
-Searchable command history (commands: "history")
-Run commands from file, save to file, edit commands in file
-Multi-line commands
-Special-character shortcut commands (beyond cmd's "?" and "!")
-Settable environment parameters
-Parsing commands with `argparse` argument parsers (flags)
-Redirection to file or paste buffer (clipboard) with > or >>
-Easy transcript-based testing of applications (see examples/transcript_example.py)
-Bash-style ``select`` available
+"""cmd2 - quickly build feature-rich and user-friendly interactive command line applications in Python.
+
+cmd2 is a tool for building interactive command line applications in Python. Its goal is to make it quick and easy for
+developers to build feature-rich and user-friendly interactive command line applications. It provides a simple API which
+is an extension of Python's built-in cmd module. cmd2 provides a wealth of features on top of cmd to make your life easier
+and eliminates much of the boilerplate code which would be necessary when using cmd.
+
+Extra features include:
+- Searchable command history (commands: "history")
+- Run commands from file, save to file, edit commands in file
+- Multi-line commands
+- Special-character shortcut commands (beyond cmd's "?" and "!")
+- Settable environment parameters
+- Parsing commands with `argparse` argument parsers (flags)
+- Redirection to file or paste buffer (clipboard) with > or >>
+- Easy transcript-based testing of applications (see examples/transcript_example.py)
+- Bash-style ``select`` available
 
 Note, if self.stdout is different than sys.stdout, then redirection with > and |
 will only work if `self.poutput()` is used in place of `print`.
 
-- Catherine Devlin, Jan 03 2008 - catherinedevlin.blogspot.com
-
-Git repository on GitHub at https://github.com/python-cmd2/cmd2
+GitHub: https://github.com/python-cmd2/cmd2
+Documentation: https://cmd2.readthedocs.io/
 """
 
 # This module has many imports, quite a few of which are only
 # infrequently utilized. To reduce the initial overhead of
 # import this module, many of these imports are lazy-loaded
 # i.e. we only import the module when we use it.
 import argparse
-import cmd
 import contextlib
 import copy
 import functools
@@ -64,7 +65,7 @@
 )
 
 import rich.box
-from rich.console import Group
+from rich.console import Group, RenderableType
 from rich.highlighter import ReprHighlighter
 from rich.rule import Rule
 from rich.style import Style, StyleType
@@ -286,7 +287,7 @@ def remove(self, command_method: CommandFunc) -> None:
             del self._parsers[full_method_name]
 
 
-class Cmd(cmd.Cmd):
+class Cmd:
     """An easy but powerful framework for writing line-oriented command interpreters.
 
     Extends the Python Standard Library's cmd package by adding a lot of useful features
@@ -304,6 +305,8 @@ class Cmd(cmd.Cmd):
     # List for storing transcript test file names
     testfiles: ClassVar[list[str]] = []
 
+    DEFAULT_PROMPT = '(Cmd) '
+
     def __init__(
         self,
         completekey: str = 'tab',
@@ -326,6 +329,7 @@ def __init__(
         auto_load_commands: bool = False,
         allow_clipboard: bool = True,
         suggest_similar_command: bool = False,
+        intro: RenderableType = '',
     ) -> None:
         """Easy but powerful framework for writing line-oriented command interpreters, extends Python's cmd package.
 
@@ -376,6 +380,7 @@ def __init__(
         :param suggest_similar_command: If ``True``, ``cmd2`` will attempt to suggest the most
                                         similar command when the user types a command that does
                                         not exist. Default: ``False``.
+        "param intro: Intro banner to print when starting the application.
         """
         # Check if py or ipy need to be disabled in this instance
         if not include_py:
@@ -384,11 +389,28 @@ def __init__(
             setattr(self, 'do_ipy', None)  # noqa: B010
 
         # initialize plugin system
-        # needs to be done before we call __init__(0)
+        # needs to be done before we most of the other stuff below
         self._initialize_plugin_system()
 
-        # Call super class constructor
-        super().__init__(completekey=completekey, stdin=stdin, stdout=stdout)
+        # Configure a few defaults
+        self.prompt = Cmd.DEFAULT_PROMPT
+        self.intro = intro
+        self.use_rawinput = True
+
+        # What to use for standard input
+        if stdin is not None:
+            self.stdin = stdin
+        else:
+            self.stdin = sys.stdin
+
+        # What to use for standard output
+        if stdout is not None:
+            self.stdout = stdout
+        else:
+            self.stdout = sys.stdout
+
+        # Key used for tab completion
+        self.completekey = completekey
 
         # Attributes which should NOT be dynamically settable via the set command at runtime
         self.default_to_shell = False  # Attempt to run unrecognized commands as shell commands
@@ -2693,10 +2715,6 @@ def postloop(self) -> None:
     def parseline(self, line: str) -> tuple[str, str, str]:
         """Parse the line into a command name and a string containing the arguments.
 
-        NOTE: This is an override of a parent class method.  It is only used by other parent class methods.
-
-        Different from the parent class method, this ignores self.identchars.
-
         :param line: line read by readline
         :return: tuple containing (command, args, line)
         """
@@ -3086,7 +3104,7 @@ def _redirect_output(self, statement: Statement) -> utils.RedirectionSavedState:
 
         # Initialize the redirection saved state
         redir_saved_state = utils.RedirectionSavedState(
-            cast(TextIO, self.stdout), stdouts_match, self._cur_pipe_proc_reader, self._redirecting
+            self.stdout, stdouts_match, self._cur_pipe_proc_reader, self._redirecting
         )
 
         # The ProcReader for this command
@@ -3141,7 +3159,7 @@ def _redirect_output(self, statement: Statement) -> utils.RedirectionSavedState:
                 new_stdout.close()
                 raise RedirectionError(f'Pipe process exited with code {proc.returncode} before command could run')
             redir_saved_state.redirecting = True
-            cmd_pipe_proc_reader = utils.ProcReader(proc, cast(TextIO, self.stdout), sys.stderr)
+            cmd_pipe_proc_reader = utils.ProcReader(proc, self.stdout, sys.stderr)
 
             self.stdout = new_stdout
             if stdouts_match:
@@ -3293,6 +3311,15 @@ def default(self, statement: Statement) -> bool | None:  # type: ignore[override
         self.perror(err_msg, style=None)
         return None
 
+    def completedefault(self, *_ignored: list[str]) -> list[str]:
+        """Call to complete an input line when no command-specific complete_*() method is available.
+
+        This method is only called for non-argparse-based commands.
+
+        By default, it returns an empty list.
+        """
+        return []
+
     def _suggest_similar_command(self, command: str) -> str | None:
         return suggest_similar(command, self.get_visible_commands())
 
@@ -4131,10 +4158,6 @@ def _build_help_parser(cls) -> Cmd2ArgumentParser:
         )
         return help_parser
 
-    # Get rid of cmd's complete_help() functions so ArgparseCompleter will complete the help command
-    if getattr(cmd.Cmd, 'complete_help', None) is not None:
-        delattr(cmd.Cmd, 'complete_help')
-
     @with_argparser(_build_help_parser)
     def do_help(self, args: argparse.Namespace) -> None:
         """List available commands or provide detailed help for a specific command."""
@@ -4640,7 +4663,7 @@ def do_shell(self, args: argparse.Namespace) -> None:
                 **kwargs,
             )
 
-            proc_reader = utils.ProcReader(proc, cast(TextIO, self.stdout), sys.stderr)
+            proc_reader = utils.ProcReader(proc, self.stdout, sys.stderr)
             proc_reader.wait()
 
             # Save the return code of the application for use in a pyscript
@@ -5359,7 +5382,7 @@ def _generate_transcript(
                 transcript += command
 
                 # Use a StdSim object to capture output
-                stdsim = utils.StdSim(cast(TextIO, self.stdout))
+                stdsim = utils.StdSim(self.stdout)
                 self.stdout = cast(TextIO, stdsim)
 
                 # then run the command and let the output go into our buffer
@@ -5385,7 +5408,7 @@ def _generate_transcript(
             with self.sigint_protection:
                 # Restore altered attributes to their original state
                 self.echo = saved_echo
-                self.stdout = cast(TextIO, saved_stdout)
+                self.stdout = saved_stdout
 
         # Check if all commands ran
         if commands_run < len(history):
@@ -5880,7 +5903,7 @@ def _report_disabled_command_usage(self, *_args: Any, message_to_print: str, **_
         """
         self.perror(message_to_print, style=None)
 
-    def cmdloop(self, intro: str | None = None) -> int:  # type: ignore[override]
+    def cmdloop(self, intro: str = '') -> int:  # type: ignore[override]
         """Deal with extra features provided by cmd2, this is an outer wrapper around _cmdloop().
 
         _cmdloop() provides the main loop equivalent to cmd.cmdloop().  This is a wrapper around that which deals with
@@ -5922,11 +5945,11 @@ def cmdloop(self, intro: str | None = None) -> int:  # type: ignore[override]
             self._run_transcript_tests([os.path.expanduser(tf) for tf in self._transcript_files])
         else:
             # If an intro was supplied in the method call, allow it to override the default
-            if intro is not None:
+            if intro:
                 self.intro = intro
 
             # Print the intro, if there is one, right after the preloop
-            if self.intro is not None:
+            if self.intro:
                 self.poutput(self.intro)
 
             # And then call _cmdloop() to enter the main loop

cmd2/py_bridge.py

@@ -137,7 +137,7 @@ def __call__(self, command: str, *, echo: bool | None = None) -> CommandResult:
                 )
         finally:
             with self._cmd2_app.sigint_protection:
-                self._cmd2_app.stdout = cast(IO[str], copy_cmd_stdout.inner_stream)
+                self._cmd2_app.stdout = cast(TextIO, copy_cmd_stdout.inner_stream)
                 if stdouts_match:
                     sys.stdout = self._cmd2_app.stdout
 

cmd2/transcript.py

@@ -46,7 +46,7 @@ def setUp(self) -> None:
 
             # Trap stdout
             self._orig_stdout = self.cmdapp.stdout
-            self.cmdapp.stdout = cast(TextIO, utils.StdSim(cast(TextIO, self.cmdapp.stdout)))
+            self.cmdapp.stdout = cast(TextIO, utils.StdSim(self.cmdapp.stdout))
 
     def tearDown(self) -> None:
         """Instructions that will be executed after each test method."""

docs/migrating/why.md

@@ -22,6 +22,11 @@ of [cmd][cmd] will add many features to an application without any further modif
 to `cmd2` will also open many additional doors for making it possible for developers to provide a
 top-notch interactive command-line experience for their users.
 
+!!! warning
+
+    As of version 4.0.0, `cmd2` does not have an actual dependency on `cmd`. `cmd2` is mostly API compatible with `cmd2`.
+    See [Incompatibilities](./incompatibilities.md) for the few documented incompatibilities.
+
 ## Automatic Features
 
 After switching from [cmd][cmd] to `cmd2`, your application will have the following new features and

mkdocs.yml

@@ -78,7 +78,6 @@ plugins:
             show_if_no_docstring: true
             preload_modules:
               - argparse
-              - cmd
             inherited_members: true
             members_order: source
             separate_signature: true

tests/test_cmd2.py

@@ -2106,6 +2106,21 @@ def make_app(isatty: bool, empty_input: bool = False):
     assert not out
 
 
+def test_custom_stdout() -> None:
+    # Create a custom file-like object (e.g., an in-memory string buffer)
+    custom_output = io.StringIO()
+
+    # Instantiate cmd2.Cmd with the custom_output as stdout
+    my_app = cmd2.Cmd(stdout=custom_output)
+
+    # Simulate a command
+    my_app.onecmd('help')
+
+    # Retrieve the output from the custom_output buffer
+    captured_output = custom_output.getvalue()
+    assert 'history' in captured_output
+
+
 def test_read_command_line_eof(base_app, monkeypatch) -> None:
     read_input_mock = mock.MagicMock(name='read_input', side_effect=EOFError)
     monkeypatch.setattr("cmd2.Cmd.read_input", read_input_mock)

tests/test_completion.py

@@ -219,14 +219,6 @@ def cmd2_app():
     return CompletionsExample()
 
 
-def test_cmd2_command_completion_single(cmd2_app) -> None:
-    text = 'he'
-    line = text
-    endidx = len(line)
-    begidx = endidx - len(text)
-    assert cmd2_app.completenames(text, line, begidx, endidx) == ['help']
-
-
 def test_complete_command_single(cmd2_app) -> None:
     text = 'he'
     line = text
@@ -322,15 +314,21 @@ def test_cmd2_command_completion_multiple(cmd2_app) -> None:
     line = text
     endidx = len(line)
     begidx = endidx - len(text)
-    assert cmd2_app.completenames(text, line, begidx, endidx) == ['help', 'history']
+
+    first_match = complete_tester(text, line, begidx, endidx, cmd2_app)
+    assert first_match is not None
+    assert cmd2_app.completion_matches == ['help', 'history']
 
 
 def test_cmd2_command_completion_nomatch(cmd2_app) -> None:
     text = 'fakecommand'
     line = text
     endidx = len(line)
     begidx = endidx - len(text)
-    assert cmd2_app.completenames(text, line, begidx, endidx) == []
+
+    first_match = complete_tester(text, line, begidx, endidx, cmd2_app)
+    assert first_match is None
+    assert cmd2_app.completion_matches == []
 
 
 def test_cmd2_help_completion_single(cmd2_app) -> None: