Nested commands

Advanced Features and Best Practices

1. Command Inheritance

You can create a base command class to share functionality:

class BaseCommand(Parser):
    def common_method(self):
        pass

class SpecificCommand(BaseCommand):
    def cli_run(self):
        self.common_method()

2. Argument Inheritance

Global arguments are accessible to subcommands:

class AppMain(Parser):
    verbose = Argument("--verbose", action="store_true")

    class SubCommand(Parser):
        def cli_run(self, verbose=False, **_):
            if verbose:
                print("Verbose mode enabled")

3. Custom Help Messages

Override the default help behavior:

def cli_run(self, **_):
    print("Custom usage information:")
    self.show_usage()
    print("\nDetailed help:")
    self.show_help()

4. Command Organization Best Practices

1. Logical Grouping:

   • Group related commands under common parents
   • Use meaningful command names
   • Keep the hierarchy shallow (3-4 levels max)

2. Argument Design:

   • Put shared options in parent commands
   • Use consistent naming across commands
   • Provide sensible defaults

3. Documentation:

   • Write clear help messages
   • Document command relationships
   • Include examples in docstrings

4. Code Structure:

   • One class per command
   • Use inheritance for shared behavior
   • Keep command implementations focused

Error Handling and Validation

1. Command Not Found:

def cli_run(self, **_):
    if not hasattr(self, 'subcommand'):
        print("No command specified")
        self.show_help()
        return 1

1. Argument Validation:

def cli_run(self, name=None, **_):
    if not name:
        print("Error: NAME is required")
        return 1

Testing Nested Commands

1. Test Command Structure:

def test_command_structure():
    app = AppMain()
    assert hasattr(app, 'command1')
    assert hasattr(app.command1, 'sub1')

1. Test Command Execution:

def test_command_execution():
    app = AppMain()
    result = app.dispatch(['command1', 'John'])
    assert result == 0