python-inject is a fast and simple to use python dependency injection framework. It uses decorators and descriptors to reference external dependencies, and scopes to specify objects life-cycles.

python-inject has been created to provide the pythonic way of dependency injection, utilizing specific Python functionality.

Links

• Project's site: http://code.google.com/p/python-inject
• User's Guide: http://code.google.com/p/python-inject/wiki/UsersGuide
• Tutorial: http://code.google.com/p/python-inject/wiki/Tutorial
• API: http://api.python-inject.googlecode.com/hg/html/index.html
• Source code: http://github.com/ivan-korobkov/python-inject

Key features

• Fast and easy to use.

• Attribute and argument injections:

  class My(object):
      attr = inject.attr(A)
      attr2 = inject.named_attr('attr2', B)
      attr3 = inject.class_attr(C)
  
  @inject.param('param', D):
  def myfunc(param):
      pass

• Normal way of instantiating objects, Class(*args, **kwargs).
• Autobinding.
• Application, thread and request scopes.
• Request scope middleware for WSGI and Django applications.
• Easy integration into existing projects.

Example

You can find this file in examples/simple.py:

"""Basic python-inject example, execute it to see the output.

All memcached, redis and mail classes are dummy classes that do not connect
to anything. They are only used to demonstrate the dependency injection
principle and python-inject functionality.
"""
import inject    

class Memcached(object):
    """Dummy memcached backend, always returns None."""
    def __init__(self, host, port):
        print 'Connected memcached to %s:%s' % (host, port)

    def get(self, key):
        """Always return None."""
        return None

class Redis(object):
    """Redis backend, always returns a new User instance for any key."""
    def __init__(self, host, port):
        print 'Connected redis to %s:%s' % (host, port)

    def get(self, key):
        return User("Ivan Korobkov", "ivan.korobkov@gmail.com")

class MailService(object):
    """Sends emails."""
    def send(self, email, text):
        """send an email."""
        print "Sent an email to %s, text=%s." % (email, text)


class User(object):

    """Example model."""

    # Both Redis and Memcached are injected as class attributes
    # so they can be accessed from the classmethods.
    redis = inject.class_attr(Redis)
    memcached = inject.class_attr(Memcached)

    # MailService is injected as a normal attribute, it can be accessed
    # only from the normal (bound) methods, not classmethods.
    mail_service = inject.attr(MailService)

    @classmethod
    def get_by_id(cls, id):
        """Get a user from memcached, if not present fallback to redis."""
        key = 'user-%s' % id
        user = cls.memcached.get(key)
        if user:
            return user
        user = cls.redis.get(key)
        print 'Loaded %s from redis.' % user
        return user

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

    def __str__(self):
        return '<User "%s">' % self.name

    @inject.param("hello_text")
    def greet(self, hello_text):
        """Send a greeting email to the user.

        @param hello_text: Demonstrates injecting params into functions. 
        """
        text = hello_text % self.name
        self.mail_service.send(self.email, text)


if __name__ == '__main__':
    """Register an injector, configure the bindings and send a greeting
    email to a user. Usually, you should store your bindings in another
    function (or functions) in another module.

    For example:
        # bindings.py
        def config(injector):
            config_redis(injector)
            config_memcached(injector)
            # etc.

        def config_redis(injector)
            redis = Redis('myhost', 1234)
            injector.bind(Redis, redis)

        def config_memached(injector):
            memcached = Memcached('myhost', 2345)
            injector.bind(Memcached, memcached)

    """
    injector = inject.Injector()
    injector.register()

    memcached = Memcached('localhost', 2345)
    redis = Redis('localhost', 1234)

    injector.bind(Redis, redis)
    injector.bind(Memcached, memcached)
    injector.bind("hello_text", "Hello, %s!")

    user = User.get_by_id(10)
    user.greet()

License

MIT License, see LICENSE.