IOC and DI service locator container implementation

components.py

from sslib import Registry
import sys


sys.modules[__name__] = Registry()

examples.py

import components


# register a factory function using the factory decorator
@components.factory("config")
def load_configuration():
  return json.load("config.json")


# register a factory class using the factory decorator
@components.factory("user_service")
class UserService:
  def find_email(self, email):
    return {"name": "test", "email": email}


# inject and use components in a function
@components.inject("config")
@components.inject("user_service")
def main(config=None, user_service=None)
  print("configuration: {!r}".format(config))
  print("user: {!r}".format(user_service.find_email("[email protected]"))

sslib.py

# coding: utf-8
import logging
from functools import wraps, partial
from pprint import pformat


log = logging.getLogger(__name__)


class SllibError(Exception):
    pass


class MissingComponentError(SllibError):
    def __init__(self, name):
        super(MissingComponentError, self).__init__(
            "missing component factory for {!r}".format(name))


class Wire:
    """
    Non-data descriptor resolving component
    """

    def __init__(self, registry, name):
        self.registry = registry
        self.name = name

    def __get__(self, obj, cls):
        if obj is None:
            return self
        instance = getattr(self.registry, self.name)
        return instance


def injector(registry, names, fn):
    @wraps(fn)
    def inner(*args, **kwargs):
        if not any(name in kwargs for name in names):
            return fn(*args, **kwargs)
        new_kwargs = kwargs.copy()
        for name in names:
            if name not in kwargs:
                new_kwargs[name] = getattr(registry, name)
        return fn(*args, **new_kwargs)
    return inner


class Container:
    """
    Service locator container.

    Create singleton container for project:

    >>> from sllib import Container
    >>> import sys
    >>> instance = Container()
    >>> instance.__file__ = __file__
    >>> sys.modules[__name__] = instance

    And inject some components into a function/method:

    >>> import components
    >>> @components.inject("config", "db")
    >>> def user_service(config=None, db=None):
    ...     pass

    Or wire some components as properties:
    
    >>> import components
    >>> class Example:
    ...     db_service = components.wire("db_service")
    ...     def find_all(self):
    ...         self.db_service.find_all()
    """

    def __init__(self):
        self.factories = {}

    def factory(self, name, factory=None):
        """
        Add factory for name.

        Use without factory param as decorator, or with factory param to add
        factory directly.

        :param name: string name of service
        :param factory: callable, optional
        """
        if factory is None:
            def inner(factory):
                self.factories[name] = factory
                return factory
            return inner
        else:
            self.factories[name] = factory

    def __getattr__(self, name):
        """
        Get instance of component or construct new instance from factory.
        """
        if name not in self.factories:
            raise MissingComponentError(name)
        factory = self.factories[name]
        instance = factory()
        log.info("initialize %r from %r", name, factory)
        setattr(self, name, instance)
        return instance

    def wire(self, name):
        """
        Wire some component as property
        
        >>> class Example:
        ...     db_service = components.wire("db_service")
        """
        return Wire(self, name)

    def inject(self, *names):
        """
        Inject some components as params
        
        >>> @components.inject("config", "db")
        >>> def example(config=None, db=None):
        ...     pass
        """
        return partial(injector, self, names)

    def __repr__(self):
        return "Registry({})".format(pformat(self.__dict__))