Modular Commands¶
Overview¶
Cmd2 also enables developers to modularize their command definitions into CommandSet
objects. CommandSets 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.
- Events handlers - Four event handlers are provided in
CommandSet
class for custom initialization and cleanup steps. See Event Handlers. - 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 API documentation for cmd2.command_definition.CommandSet
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 can 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_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()
Event Handlers¶
The following functions are called at different points in the CommandSet
life cycle.
on_register(self, cmd) -> None
- Called by cmd2.Cmd as the first step to
registering a CommandSet. The commands defined in this class have not be
added to the CLI object at this point. Subclasses can override this to
perform any initialization requiring access to the Cmd object
(e.g. configure commands and their parsers based on CLI state data).
on_registered(self) -> None
- Called by cmd2.Cmd after a CommandSet is
registered and all its commands have been added to the CLI. Subclasses can
override this to perform custom steps related to the newly added commands
(e.g. setting them to a disabled state).
on_unregister(self) -> None
- Called by cmd2.Cmd
as the first step to
unregistering a CommandSet. Subclasses can override this to perform any cleanup
steps which require their commands being registered in the CLI.
on_unregistered(self) -> None
- Called by cmd2.Cmd
after a CommandSet
has been unregistered and all its commands removed from the CLI. Subclasses can
override this to perform remaining cleanup steps.
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()
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()
bokchoy_parser.add_argument('style', choices=['quartered', 'diced'])
@cmd2.as_subcommand_to('cut', 'bokchoy', bokchoy_parser)
def cut_bokchoy(self, _: argparse.Namespace):
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_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_subparsers = cut_parser.add_subparsers(title='item', help='item to cut')
@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()