Documentation doesn't describe "lazy loading of subcommands at runtime"

[ncraike]

The documentation home page includes:

Click in three points:

• arbitrary nesting of commands
• automatic help page generation
• supports lazy loading of subcommands at runtime

How is "lazy-loading of subcommands at runtime" supported? The various methods of creating command groups and attaching sub-commands described in the quickstart guide all require importing the sub-command first.

The closest I can find is a demonstration of how lazy-loading of commands from plugins might be implemented with a custom multi-command class. Is this the "lazy loading of subcommands at runtime" which the documentation describes?

[ThiefMaster]

I think so. Another way do do lazy loading would be something like this: https://github.com/indico/indico/blob/master/indico/cli/util.py#L95 / https://github.com/indico/indico/blob/master/indico/cli/core.py#L68

[scoopex]

Yes this would be a good thing. In larger implementation long import times especially effect the snappiness of shell completion. (my project with 16 command groups, takes 2.5 seconds for a completion step....)

[BernardZhao]

I also found this quite misleading, can this third point be removed from the docs? There doesn't seem to be anything in Click that does this out of the box

[wonderbeyond]

I've implemented lazy sub-commands in my way, FYI.

import sys
from importlib import import_module

from my_project.db import alembic
import click


def import_from_string(spec):
    """
    Thanks to https://github.com/encode/django-rest-framework/blob/master/rest_framework/settings.py#L170
    Example:
        import_from_string('django_filters.rest_framework.DjangoFilterBackend')
        engine = conf['ENGINE']
        engine = import_from_string(engine) if isinstance(engine, six.string_types) else engine
    """
    try:
        # Nod to tastypie's use of importlib.
        parts = spec.split('.')
        module_path, class_name = '.'.join(parts[:-1]), parts[-1]
        module = import_module(module_path)
        return getattr(module, class_name)
    except (ImportError, AttributeError) as e:
        msg = "Could not import '%s'. %s: %s." % (spec, e.__class__.__name__, e)
        raise ImportError(msg)


@click.group()
def manager():
    """MyProject Management Tools."""


def get_db_cmd():
    db_cmd = alembic.get_click_cli("db")
    db_cmd.help = 'Design database schema with confidence.'
    return db_cmd


cmd_factories = dict((
    ('db', get_db_cmd),
    ('dev', lambda: import_from_string('my_project.commands.dev.dev')),
    ('shell', lambda: import_from_string('my_project.commands.shell.shell')),
    ('psql', lambda: import_from_string('my_project.commands.psql.psql')),
    ('protoc', lambda: import_from_string('my_project.commands.protoc.protoc')),
    ('cache', lambda: import_from_string('my_project.commands.cache.cache')),
    ('test', lambda: import_from_string('my_project.commands.testing.test')),
    ...
))

if __name__ == '__main__':
    if len(sys.argv) > 1 and (cmd_name := sys.argv[1]) in cmd_factories:
        # Construct sub-command only as needed.
        manager.add_command(cmd_factories[cmd_name](), name=cmd_name)
    else:
        # For user can list all sub-commands.
        for cmd_name, fct in cmd_factories.items():
            manager.add_command(fct(), name=cmd_name)

    manager()

[davidism]

Fixed by https://github.com/pallets/click/pull/2348, can be found at https://click.palletsprojects.com/complex/#lazily-loading-subcommands