Fix bug where tab completion didn't work in embedded Python shell when LibEdit was insalled instead of readline

Author: tleonhardt

cmd2/cmd2.py

@@ -183,6 +183,7 @@ class _SavedCmd2Env:
 
     def __init__(self) -> None:
         self.history: list[str] = []
+        self.completer: Callable[[str, int], str | None] | None = None
 
 
 # Contains data about a disabled command which is used to restore its original functions when the command is enabled
@@ -4593,7 +4594,7 @@ def _reset_py_display() -> None:
         sys.displayhook = sys.__displayhook__
         sys.excepthook = sys.__excepthook__
 
-    def _set_up_py_shell_env(self, _interp: InteractiveConsole) -> _SavedCmd2Env:
+    def _set_up_py_shell_env(self, interp: InteractiveConsole) -> _SavedCmd2Env:
         """Set up interactive Python shell environment.
 
         :return: Class containing saved up cmd2 environment.
@@ -4603,13 +4604,39 @@ def _set_up_py_shell_env(self, _interp: InteractiveConsole) -> _SavedCmd2Env:
         # Set up sys module for the Python console
         self._reset_py_display()
 
+        # Enable tab completion if readline is available
+        try:
+            import readline
+            import rlcompleter
+        except ImportError:
+            pass
+        else:
+            # Save the current completer
+            cmd2_env.completer = readline.get_completer()
+
+            # Set the completer to use the interpreter's locals
+            readline.set_completer(rlcompleter.Completer(interp.locals).complete)
+
+            # Use the correct binding based on whether LibEdit or Readline is being used
+            if 'libedit' in (readline.__doc__ or ''):
+                readline.parse_and_bind("bind ^I rl_complete")
+            else:
+                readline.parse_and_bind("tab: complete")
+
         return cmd2_env
 
-    def _restore_cmd2_env(self, _cmd2_env: _SavedCmd2Env) -> None:
+    def _restore_cmd2_env(self, cmd2_env: _SavedCmd2Env) -> None:
         """Restore cmd2 environment after exiting an interactive Python shell.
 
         :param cmd2_env: the environment settings to restore
         """
+        # Restore the readline completer
+        try:
+            import readline
+        except ImportError:
+            pass
+        else:
+            readline.set_completer(cmd2_env.completer)
 
     def _run_python(self, *, pyscript: str | None = None) -> bool | None:
         """Run an interactive Python shell or execute a pyscript file.

examples/basic_completion.py

@@ -33,7 +33,7 @@
 
 class BasicCompletion(cmd2.Cmd):
     def __init__(self) -> None:
-        super().__init__(complete_style=CompleteStyle.MULTI_COLUMN)
+        super().__init__(complete_style=CompleteStyle.MULTI_COLUMN, include_py=True)
 
     def do_flag_based(self, statement: cmd2.Statement) -> None:
         """Tab completes arguments based on a preceding flag using flag_based_complete

tests/test_py_completion.py

@@ -0,0 +1,50 @@
+import sys
+from code import InteractiveConsole
+from unittest import mock
+
+
+def test_py_completion_setup_readline(base_app):
+    # Mock readline and rlcompleter
+    mock_readline = mock.MagicMock()
+    mock_readline.__doc__ = 'GNU Readline'
+    mock_rlcompleter = mock.MagicMock()
+
+    with mock.patch.dict(sys.modules, {'readline': mock_readline, 'rlcompleter': mock_rlcompleter}):
+        interp = InteractiveConsole()
+        base_app._set_up_py_shell_env(interp)
+
+        # Verify completion setup for GNU Readline
+        mock_readline.parse_and_bind.assert_called_with("tab: complete")
+        mock_readline.set_completer.assert_called()
+
+
+def test_py_completion_setup_libedit(base_app):
+    # Mock readline and rlcompleter
+    mock_readline = mock.MagicMock()
+    mock_readline.__doc__ = 'libedit'
+    mock_rlcompleter = mock.MagicMock()
+
+    with mock.patch.dict(sys.modules, {'readline': mock_readline, 'rlcompleter': mock_rlcompleter}):
+        interp = InteractiveConsole()
+        base_app._set_up_py_shell_env(interp)
+
+        # Verify completion setup for LibEdit
+        mock_readline.parse_and_bind.assert_called_with("bind ^I rl_complete")
+        mock_readline.set_completer.assert_called()
+
+
+def test_py_completion_restore(base_app):
+    # Mock readline
+    mock_readline = mock.MagicMock()
+    original_completer = mock.Mock()
+    mock_readline.get_completer.return_value = original_completer
+
+    with mock.patch.dict(sys.modules, {'readline': mock_readline, 'rlcompleter': mock.MagicMock()}):
+        interp = InteractiveConsole()
+        env = base_app._set_up_py_shell_env(interp)
+
+        # Restore and verify
+        base_app._restore_cmd2_env(env)
+
+        # set_completer is called twice: once in setup, once in restore
+        mock_readline.set_completer.assert_called_with(original_completer)