subparse

A wrapper for argparse that provides decorator-based subcommand support.

Commands can be defined separately from their actual main functions, enabling faster import times.

Basic Usage

from subparse import CLI

class MyApp(object):
    def __init__(self, quiet=False):
        self.quiet = quiet

    def info(self, *msg):
        if not self.quiet:
            print('[info]', *msg)

def context_factory(cli, args):
    return MyApp(args.quiet)

def generic_options(parser):
    parser.add_argument('--quiet', action='store_true',
                        help='turn of debugging')

cli = CLI(version='0.0', context_factory=context_factory)
cli.add_generic_options(generic_options)

@cli.command(__name__ + ':foo_main')
def foo(parser):
    """
    a short description ending in a period.

    a longer description
    """
    parser.add_argument('--bar', action='store_true',
                        help='turn on bar')

def foo_main(app, args):
    app.info('Hello World!')

result = cli.run()
sys.exit(result)

Lazy Decorators

Commands can be defined lazily and picked up later. This removes ordering restrictions between the commands and the cli object.

A module containing commands can be defined irrespective of the actual CLI instance:

# myapp/info.py

from subparse import command

@command('myapp.info:foo_main')
def foo(parser):
    """perform foo"""

Later, when an instance of a CLI is created, the commands can be loaded and registered:

cli = CLI()
cli.load_commands('myapp.info')

Entry Points

Commands may also be defined in external modules and loaded via entry points.

from subparse import cli

cli = CLI()
cli.load_commands_from_entry_point('myapp.commands')

An extension application would then define the external module that should be searched for commands. Again this allows the commands themselves to be defined independently of the main functions, improving import speed.

An extension package should define a module containing the supported commands:

# barpkg/commands.py

from subparse import command

@command('barpkg.bar')
def bar(parser):
    """perform bar"""

The package should also define the function to be called for each command. Optionally in a separate module to avoid importing run-time dependencies during parsing:

# barpkg/bar.py

def main(app, args):
    pass

The package can then broadcast the module barpkg.commands containing the supported commands:

[myapp.commands]
barpkg = barpkg.commands

Now when your extension package is installed the commands will automatically become available.

Context Factory

Each subcommand, when executed, is passed a context object which defines a reusable API between subcommands. This is really the secret sauce of subparse that makes it really easy to build your own shared CLI features.

The context_factory argument to the subparse.CLI allows for defining an object that is passed to all commands. This factory can also be a generator, allowing it to yield the context object and then cleanup after the command is complete. For example:

import transaction

def context_factory(cli, args):
    tm = transaction.TransactionManager(explicit=True)
    with tm:
        yield tm

In the above example the transaction manager is available to all subcommands and it can commit/abort based on whether the command raises an exception.

Each subcommand can pass custom kwargs to the context factory via the context_kwargs argument. For example, if a single subcommand wishes to opt-out of the transaction manager:

def context_factory(cli, args, without_tm=False):
    if without_tm:
        yield

    tm = transaction.TransactionManager(explicit=True)
    with tm:
        yield tm

@command(..., context_kwargs=dict(without_tm=True))
def foo(parser):
    """" Run a command without the tm enabled."""