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Type-based dependency injection

Project description

.. figure:: https://github.com/Dobiasd/enterprython/raw/master/logo/enterprython.png :alt: logo

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|Build Status| |(License MIT 1.0)|

enterprython

Python library providing type-based dependency injection

Table of contents

  • Introduction <#introduction>__
  • Features <#features>__
  • Abstract base classes <#abstract-base-classes>__
  • Factories <#factories>__
  • Non-singleton services <#non-singleton-services>__
  • Service lists <#service-lists>__
  • Mixing managed and manual injection <#mixing-managed-and-manual-injection>__
  • Free functions as clients <#free-functions-as-clients>__
  • Requirements and Installation <#requirements-and-installation>__

Introduction

If you plan to develop SOLID <https://en.wikipedia.org/wiki/SOLID>__ / domain-driven <https://en.wikipedia.org/wiki/Domain-driven_design>__ (i.e., enterprisey) software, you probably want <why_you_want_formal_dependency_injection_in_python_too.md>__ to apply inversion of control <https://en.wikipedia.org/wiki/Inversion_of_control>__ in the form of dependency injection <https://en.wikipedia.org/wiki/Dependency_injection>__ when writing the constructors of your classes. Also you likely want to use a library doing the needed lookups for you based on static type annotations, instead of manually configuring the object graph.

enterprython provides exactly that.

.. code:: python

from enterprython import assemble, component

@component()
class Service:
    def __init__(self) -> None:
        self._greeting: str = 'Hello'

    def greet(self, name: str) -> str:
        return f'{self._greeting}, {name}!'

class Client:
    def __init__(self, service: Service) -> None:
        self._service = service

    def run(self) -> None:
        print(self._service.greet('World'))


assemble(Client).run()

Output:

.. code:: text

Hello, World!

Features

Abstract base classes


A client may depend on an abstract base class. Enterprython will inject
the matching implementation.

.. code:: python

    from abc import ABC
    from enterprython import assemble, component

    class ServiceInterface(ABC):
        ...

    @component()
    class ServiceImpl(ServiceInterface):
        ...

    class Client:
        def __init__(self, services: ServiceInterface) -> None:
            ...

    assemble(Client)

One singleton instance of ``ServiceImpl`` is created and injected into
``Client``.

Factories
~~~~~~~~~

Annotating a function with ``@factory()`` registers a factory for its
return type.

.. code:: python


    from enterprython import assemble, component

    class Service:
        ...

    @factory()
    def service_factory() -> Service:
        return Service()

    class Client:
        def __init__(self, service: Service) -> None:
            ...

    assemble(Client)

``service_factory`` is used to create the ``Service`` instance for
calling the constructor of ``Client``.

Non-singleton services

If a service is annotated with @component(singleton=False) a new instance of it is created with every injection.

.. code:: python

@component(singleton=False)
class Service:
    ...

class Client:
    def __init__(self, service: Service) -> None:
        ...

Service lists


A client may depend on a list of implementations of a service interface.

.. code:: python

    from abc import ABC
    from typing import List
    from enterprython import assemble, component

    class ServiceInterface(ABC):
        pass

    @component()
    class ServiceA(ServiceInterface):
        ...

    @component()
    class ServiceB(ServiceInterface):
        ...

    class Client:
        def __init__(self, services: List[ServiceInterface]) -> None:
            ...

    assemble(Client)

``[ServiceA(), ServiceB()]`` is injected into ``Client``.

Mixing managed and manual injection

One part of a client's dependencies might be injected manually, the rest automatically.

.. code:: python

from enterprython import assemble, component

@component()
class ServiceA:
    ...

class ServiceB:
    ...

class Client:
    def __init__(self, service_a: ServiceA, service_b: ServiceB) -> None:
        ...

assemble(Client, service_b=ServiceB())

service_a comes from the DI container, service_b from user code.

If ServiceB also has a @component() annotation, the manually provided object is preferred.

Free functions as clients


Since class constructors are fundamentally just normal functions, we can
inject dependencies into free functions too.

.. code:: python


    from enterprython import assemble, component

    @component()
    class Service:
        ...

    def client(service: Service) -> None:
        ...

    assemble(client)

A singleton instance of ``Service`` is created and used to call
``client``.

Requirements and Installation
-----------------------------

You need Python 3.6.5 or higher.

.. code:: bash

    python3 -m pip install enterprython

Or, if you like to use latest version from this repository:

.. code:: bash

    git clone https://github.com/Dobiasd/enterprython
    cd enterprython
    python3 -m pip install .

License
-------

Distributed under the MIT License. (See accompanying file
```LICENSE`` <https://github.com/Dobiasd/enterprython/blob/master/LICENSE>`__
or at https://opensource.org/licenses/MIT)

.. |Build Status| image:: https://travis-ci.org/Dobiasd/enterprython.svg?branch=master
   :target: https://travis-ci.org/Dobiasd/enterprython
.. |(License MIT 1.0)| image:: https://img.shields.io/badge/license-MIT%201.0-blue.svg
   :target: LICENSE


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