weenect / weedi

Weenect Python Dependency Injection System

Weedi

Introduction

Weedi is a dependency injection container based on setuptools and entry points.

It was first developed by Net-ng and later opensourced and maintained by Weenect.

It is tested for python's versions 2.7, 3.3, 3.4 and 3.5

• Link on Pypi

Installation

You will need to have setuptools installed and to use it in your project as weedi uses the entry_points feature.

You can add weedi as a dependency of your project in your setup.py :

from setuptools import setup, find_packages

setup(
    ...
    install_requires=('weedi'),
    ...
)

Then run python setup.py install or python setup.py develop

Usage

Let's suppose you are managing locators and you have a service LocatorManager which depends on the database.

You will have these class in a module services.py :

import weedi.loadable as loadable


class Database(loadable.Service):
    spec = {
        'host': 'string(default="localhost")',
        'port': 'integer(default=3306)',
        'debug': 'boolean(default=False)',
    }

    load_priority = -10

    def __init__(self, host, port, debug):
        self.host = host
        self.port = port
        self.debug = debug


class LocatorManager(loadable.Service):
    def __init__(self, database_service):
        self.db = database_service

Your services needs to extend ``weedi.loadable.Loadable``. If not, just provide 2 class attributes : ``load_priority`` and ``spec``*

You need to register these services in the entry_points or your project setup.py.

setup(
    ...
    entry_points='''
        [services]
        database = my_project.services:Database
        manager = my_project.services:LocatorManager
    '''
    ...
)

Note : the name of the argument in LocatorManager constructor is database_service. This is the concatenation of the code of the database entry point and the string ``_service``. This is the way the library recognizes that it needs to inject the database service when it instanciates the manager service.

Then, you need to configure your container. Let's create a module repository.py. When creating a container, you need to define the name of the section managed by this repository in the entry points (here, it will be services) and the name of the section in the config file for this repository (cf config.ini below, it will be services too).

import weedi.loadables_repository as loadables_repository


class ServicesRepository(loadables_repository.LoadablesRepository):
    entry_point = 'services'
    conf_section = 'services'

The database service will have default value injected when it is created based on its spec. You can override this by creating a config file config.ini :

[services]

[[database]]
host = "database.local"
port = 5432
debug = True

Everything is ready. You just have to start your container.

service_repository = ServicesRepository()
service_repository.load('path_to/config.ini')

You can access the services from the container :

database_service = service_repository['database']
locator_manager_service = service_repository['manager']

You can inject these services in an object by constructor or by method :

class ObjectNeedsService(object):
  def __init__(self, database_service):
    self.db = database_service
    self.manager = None

  def set_services(self, manager_service):
    self.manager = manager_service

new_instance = service_repository(ObjectNeedsService)
assert new_instance.db == service_repository['database']
assert new_instance.manager is None
service_repository(new_instance.set_services)
assert new_instance.db == service_repository['database']
assert new_instance.manager == service_repository['manager']

You can pass arguments to the called function when using the container :

class ObjectWithArgs(object):
  def __init__(self, param1, param2, database_service, param3=None, param4={}):
    self.db = database_service
    self.param1 = param1
    self.param2 = param2
    self.param3 = param3
    self.param4 = param4

new_instance = service_repository(ObjectWithArgs, 'param1', 'param2', param4='param4')
assert new_instance.db == service_repository['database']
assert new_instance.param1 == 'param1'
assert new_instance.param2 == 'param2'
assert new_instance.param3 is None
assert new_instance.param4 == 'param4'

The ``project`` folder is used to both run functional tests and to provide examples of use cases. Don't hesitate to go see the test cases : https://github.com/weenect/weedi/blob/master/project/project/tests.py

Troubleshooting.

• You are getting an exception ServiceWrongPriority : change the load_priority value of your services to change the order of instanciation. The lesser the value is, the sooner it is instanciated.
• You are getting an exception ServiceMissing : you forgot to define (or mispelled) a service definition in your project entry points.
• You are getting an exception WrongConfiguration : You are missing some configuration key for a service in your config file or you are missing a config file altogether.