Modular Commands

Overview

Cmd2 also enables developers to modularize their command definitions into Command Sets. Command sets represent a logical grouping of commands within an cmd2 application. By default, all CommandSets will be discovered and loaded automatically when the cmd2.Cmd class is instantiated with this mixin. This also enables the developer to dynamically add/remove commands from the cmd2 application. This could be useful for loadable plugins that add additional capabilities. Additionally, it allows for object-oriented encapsulation and garbage collection of state that is specific to a CommandSet.

Features

  • Modular Command Sets - Commands can be broken into separate modules rather than in one god class holding all commands.
  • Automatic Command Discovery - In your application, merely defining and importing a CommandSet is sufficient for cmd2 to discover and load your command. No manual registration is necessary.
  • Dynamically Loadable/Unloadable Commands - Command functions and CommandSets can both be loaded and unloaded dynamically during application execution. This can enable features such as dynamically loaded modules that add additional commands.
  • Subcommand Injection - Subcommands can be defined separately from the base command. This allows for a more action-centric instead of object-centric command system while still organizing your code and handlers around the objects being managed.

See the examples for more details: https://github.com/python-cmd2/cmd2/tree/master/plugins/command_sets/examples

Defining Commands

Command Sets

CommandSets group multiple commands together. The plugin will inspect functions within a CommandSet using the same rules as when they’re defined in cmd2.Cmd. Commands must be prefixed with do_, help functions with help_, and completer functions with complete_.

A new decorator with_default_category is provided to categorize all commands within a CommandSet in the same command category. Individual commands in a CommandSet may be override the default category by specifying a specific category with cmd.with_category.

CommandSet command methods will always expect the same parameters as when defined in a cmd2.Cmd sub-class, except that self will now refer to the CommandSet instead of the cmd2 instance. The cmd2 instance can be accessed through self._cmd that is populated when the CommandSet is registered.

CommandSets will only be auto-loaded if the constructor takes no arguments. If you need to provide constructor arguments, see Manual CommandSet Construction

import cmd2
from cmd2 import CommandSet, with_default_category

@with_default_category('My Category')
class AutoLoadCommandSet(CommandSet):
    def __init__(self):
        super().__init__()

    def do_hello(self, _: cmd2.Statement):
        self._cmd.poutput('Hello')

    def do_world(self, _: cmd2.Statement):
        self._cmd.poutput('World')

class ExampleApp(cmd2.Cmd):
    """
    CommandSets are automatically loaded. Nothing needs to be done.
    """
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

    def do_something(self, arg):
        self.poutput('this is the something command')

Manual CommandSet Construction

If a CommandSet class requires parameters to be provided to the constructor, you man manually construct CommandSets and pass in the constructor to Cmd2.

import cmd2
from cmd2 import CommandSet, with_default_category

@with_default_category('My Category')
class CustomInitCommandSet(CommandSet):
    def __init__(self, arg1, arg2):
        super().__init__()

        self._arg1 = arg1
        self._arg2 = arg2

    def do_show_arg1(self, _: cmd2.Statement):
        self._cmd.poutput('Arg1: ' + self._arg1)

    def do_show_arg2(self, _: cmd2.Statement):
        self._cmd.poutput('Arg2: ' + self._arg2)

class ExampleApp(cmd2.Cmd):
    """
    CommandSets with constructor parameters are provided in the constructor
    """
    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, **kwargs)

    def do_something(self, arg):
        self.last_result = 5
        self.poutput('this is the something command')


def main():
    my_commands = CustomInitCommandSet(1, 2)
    app = ExampleApp(command_sets=[my_commands])
    app.cmdloop()

Dynamic Commands

You man also dynamically load and unload commands by installing and removing CommandSets at runtime. For example, if you could support runtime loadable plugins or add/remove commands based on your state.

You may need to disable command auto-loading if you need dynamically load commands at runtime.

import argparse
import cmd2
from cmd2 import CommandSet, with_argparser, with_category, with_default_category


@with_default_category('Fruits')
class LoadableFruits(CommandSet):
    def __init__(self):
        super().__init__()

    def do_apple(self, _: cmd2.Statement):
        self._cmd.poutput('Apple')

    def do_banana(self, _: cmd2.Statement):
        self._cmd.poutput('Banana')


@with_default_category('Vegetables')
class LoadableVegetables(CommandSet):
    def __init__(self):
        super().__init__()

    def do_arugula(self, _: cmd2.Statement):
        self._cmd.poutput('Arugula')

    def do_bokchoy(self, _: cmd2.Statement):
        self._cmd.poutput('Bok Choy')


class ExampleApp(cmd2.Cmd):
    """
    CommandSets are loaded via the `load` and `unload` commands
    """

    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, auto_load_commands=False, **kwargs)

        self._fruits = LoadableFruits()
        self._vegetables = LoadableVegetables()

    load_parser = cmd2.Cmd2ArgumentParser('load')
    load_parser.add_argument('cmds', choices=['fruits', 'vegetables'])

    @with_argparser(load_parser)
    @with_category('Command Loading')
    def do_load(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            try:
                self.register_command_set(self._fruits)
                self.poutput('Fruits loaded')
            except ValueError:
                self.poutput('Fruits already loaded')

        if ns.cmds == 'vegetables':
            try:
                self.register_command_set(self._vegetables)
                self.poutput('Vegetables loaded')
            except ValueError:
                self.poutput('Vegetables already loaded')

    @with_argparser(load_parser)
    def do_unload(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            self.unregister_command_set(self._fruits)
            self.poutput('Fruits unloaded')

        if ns.cmds == 'vegetables':
            self.unregister_command_set(self._vegetables)
            self.poutput('Vegetables unloaded')


if __name__ == '__main__':
    app = ExampleApp()
    app.cmdloop()

Injecting Subcommands

Description

Using the with_argparse decorator, it is possible to define subcommands for your command. This has a tendency to either drive your interface into an object-centric interface. For example, imagine you have a tool that manages your media collection and you want to manage movies or shows. An object-centric approach would push you to have base commands such as movies and shows which each have subcommands add, edit, list, delete. If you wanted to present an action-centric command set, so that add, edit, list, and delete are the base commands, you’d have to organize your code around these similar actions rather than organizing your code around similar objects being managed.

Subcommand injection allows you to inject subcommands into a base command to present an interface that is sensible to a user while still organizing your code in whatever structure make more logical sense to the developer.

Example

This example is a variation on the Dynamic Commands example above. A cut command is introduced as a base command and each CommandSet

import argparse
import cmd2
from cmd2 import CommandSet, with_argparser, with_category, with_default_category


@with_default_category('Fruits')
class LoadableFruits(CommandSet):
    def __init__(self):
        super().__init__()

    def do_apple(self, _: cmd2.Statement):
        self._cmd.poutput('Apple')

    banana_parser = cmd2.Cmd2ArgumentParser(add_help=False)
    banana_parser.add_argument('direction', choices=['discs', 'lengthwise'])

    @cmd2.as_subcommand_to('cut', 'banana', banana_parser)
    def cut_banana(self, ns: argparse.Namespace):
        """Cut banana"""
        self._cmd.poutput('cutting banana: ' + ns.direction)


@with_default_category('Vegetables')
class LoadableVegetables(CommandSet):
    def __init__(self):
        super().__init__()

    def do_arugula(self, _: cmd2.Statement):
        self._cmd.poutput('Arugula')

    bokchoy_parser = cmd2.Cmd2ArgumentParser(add_help=False)
    bokchoy_parser.add_argument('style', choices=['quartered', 'diced'])

    @cmd2.as_subcommand_to('cut', 'bokchoy', bokchoy_parser)
    def cut_bokchoy(self, _: cmd2.Statement):
        self._cmd.poutput('Bok Choy')


class ExampleApp(cmd2.Cmd):
    """
    CommandSets are automatically loaded. Nothing needs to be done.
    """

    def __init__(self, *args, **kwargs):
        # gotta have this or neither the plugin or cmd2 will initialize
        super().__init__(*args, auto_load_commands=False, **kwargs)

        self._fruits = LoadableFruits()
        self._vegetables = LoadableVegetables()

    load_parser = cmd2.Cmd2ArgumentParser('load')
    load_parser.add_argument('cmds', choices=['fruits', 'vegetables'])

    @with_argparser(load_parser)
    @with_category('Command Loading')
    def do_load(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            try:
                self.register_command_set(self._fruits)
                self.poutput('Fruits loaded')
            except ValueError:
                self.poutput('Fruits already loaded')

        if ns.cmds == 'vegetables':
            try:
                self.register_command_set(self._vegetables)
                self.poutput('Vegetables loaded')
            except ValueError:
                self.poutput('Vegetables already loaded')

    @with_argparser(load_parser)
    def do_unload(self, ns: argparse.Namespace):
        if ns.cmds == 'fruits':
            self.unregister_command_set(self._fruits)
            self.poutput('Fruits unloaded')

        if ns.cmds == 'vegetables':
            self.unregister_command_set(self._vegetables)
            self.poutput('Vegetables unloaded')

    cut_parser = cmd2.Cmd2ArgumentParser('cut')
    cut_subparsers = cut_parser.add_subparsers(title='item', help='item to cut', unloadable=True)

    @with_argparser(cut_parser)
    def do_cut(self, ns: argparse.Namespace):
        handler = ns.cmd2_handler.get()
        if handler is not None:
            # Call whatever subcommand function was selected
            handler(ns)
        else:
            # No subcommand was provided, so call help
            self.poutput('This command does nothing without sub-parsers registered')
            self.do_help('cut')


if __name__ == '__main__':
    app = ExampleApp()
    app.cmdloop()