Merge pull request #647 from python-cmd2/help_error

Help now writes to stderr when no help information is found

Author: kmvanbrunt

CHANGELOG.md

@@ -2,6 +2,17 @@
 * Enhancements
     * Added ability to include command name placeholders in the message printed when trying to run a disabled command.
         * See docstring for ``disable_command()`` or ``disable_category()`` for more details.
+    * Added instance attributes to customize error messages without having to override methods. Theses messages can
+    also be colored.
+        * `help_error` - the error that prints when no help information can be found
+        * `default_error` - the error that prints when a non-existent command is run
+* Potentially breaking changes
+    * The following commands now write to stderr instead of stdout when printing an error. This will make catching
+    errors easier in pyscript.
+        * ``do_help()`` - when no help information can be found
+        * ``default()`` - in all cases since this is called when an invalid command name is run
+        * ``_report_disabled_command_usage()`` - in all cases since this is called when a disabled command is run
+    * Removed *** from beginning of error messages printed by `do_help()` and `default()`.
 
 ## 0.9.11 (March 13, 2019)
 * Bug Fixes

cmd2/cmd2.py

@@ -428,6 +428,12 @@ def __init__(self, completekey: str = 'tab', stdin=None, stdout=None, persistent
         # Used to keep track of whether a continuation prompt is being displayed
         self.at_continuation_prompt = False
 
+        # The error that prints when no help information can be found
+        self.help_error = "No help on {}"
+
+        # The error that prints when a non-existent command is run
+        self.default_error = "{} is not a recognized command, alias, or macro"
+
         # If this string is non-empty, then this warning message will print if a broken pipe error occurs while printing
         self.broken_pipe_warning = ''
 
@@ -2057,8 +2063,8 @@ def default(self, statement: Statement) -> Optional[bool]:
 
             return self.do_shell(statement.command_and_args)
         else:
-            self.perror('*** {} is not a recognized command, alias, or macro'.format(statement.command),
-                        err_color=Fore.RESET, traceback_war=False)
+            err_msg = self.default_error.format(statement.command)
+            self.decolorized_write(sys.stderr, "{}\n".format(err_msg))
 
     def pseudo_raw_input(self, prompt: str) -> str:
         """Began life as a copy of cmd's cmdloop; like raw_input but
@@ -2586,12 +2592,21 @@ def do_help(self, args: argparse.Namespace) -> None:
         else:
             # Getting help for a specific command
             func = self.cmd_func(args.command)
+            help_func = getattr(self, HELP_FUNC_PREFIX + args.command, None)
+
+            # If the command function uses argparse, then use argparse's help
             if func and hasattr(func, 'argparser'):
                 completer = AutoCompleter(getattr(func, 'argparser'), self)
                 tokens = [args.command] + args.subcommand
                 self.poutput(completer.format_help(tokens))
+
+            # If there is no help information then print an error
+            elif help_func is None and (func is None or not func.__doc__):
+                err_msg = self.help_error.format(args.command)
+                self.decolorized_write(sys.stderr, "{}\n".format(err_msg))
+
+            # Otherwise delegate to cmd base class do_help()
             else:
-                # No special behavior needed, delegate to cmd base class do_help()
                 super().do_help(args.command)
 
     def _help_menu(self, verbose: bool = False) -> None:
@@ -3719,7 +3734,7 @@ def _report_disabled_command_usage(self, *args, message_to_print: str, **kwargs)
         :param message_to_print: the message reporting that the command is disabled
         :param kwargs: not used
         """
-        self.perror(message_to_print, err_color=Fore.RESET, traceback_war=False)
+        self.decolorized_write(sys.stderr, "{}\n".format(message_to_print))
 
     def cmdloop(self, intro: Optional[str] = None) -> None:
         """This is an outer wrapper around _cmdloop() which deals with extra features provided by cmd2.

tests/test_cmd2.py

@@ -952,10 +952,10 @@ def test_custom_help_menu(help_app):
 """)
     assert out == expected
 
-def test_help_undocumented(help_app):
-    out = run_cmd(help_app, 'help undoc')
-    expected = normalize('*** No help on undoc')
-    assert out == expected
+def test_help_undocumented(help_app, capsys):
+    run_cmd(help_app, 'help undoc')
+    out, err = capsys.readouterr()
+    assert err.startswith("No help on undoc")
 
 def test_help_overridden_method(help_app):
     out = run_cmd(help_app, 'help edit')
@@ -1787,8 +1787,9 @@ def test_macro_create_with_escaped_args(base_app, capsys):
     assert out == normalize("Macro 'fake' created")
 
     # Run the macro
-    out = run_cmd(base_app, 'fake')
-    assert 'No help on {1}' in out[0]
+    run_cmd(base_app, 'fake')
+    out, err = capsys.readouterr()
+    assert err.startswith('No help on {1}')
 
 def test_macro_usage_with_missing_args(base_app, capsys):
     # Create the macro