Implementation of dependency injection for Python 3
Project description
Implementation of dependency injection for Python 3
Features:
- types resolution by signature types annotations (type hints)
- types resolution by class annotations (type hints)
- types resolution by names and aliases (convention over configuration)
- unintrusive: builds objects graph without the need to change the source code of classes
- minimum overhead to obtain services, once the objects graph is built
- support for singletons, transient, and scoped services
This library is freely inspired by .NET Standard
Microsoft.Extensions.DependencyInjection
implementation (ref. MSDN,
Dependency injection in ASP.NET
Core,
Using dependency injection in a .Net Core console
application).
The ContainerProtocol
for v2 is inspired by punq.
Installation
pip install neoteroi-di
neoteroi-di
is the new version of the library that was previously named
rodi
. It is currently alpha
and still
subject to change.
Efficient
neoteroi-di
works by inspecting code once at runtime, to generate
functions that return instances of desired types - as long as the object graph
is not altered. Inspections are done either on constructors
(__init__) or class annotations. Validation steps, for
example to detect circular dependencies or missing services, are done when
building these functions, so additional validation is not needed when
activating services.
Flexible
neoteroi-di
offers two code APIs:
- one is kept as generic as possible, using a
ContainerProtocol
for scenarios in which it is desirable being able to replaceneoteroi-di
with alternative implementations of dependency injection for Python. The protocol only expects a class being able toregister
andresolve
types, and to tell if a type is configured in it (__contains__
). Even if other implementations of DI don´t implement these three methods, it should be easy to use composition to wrap other libraries with a compatible class. - one is a more concrete implementation, following the previous implementation
in
rodi
, for scenarios where it's not desirable to consider alternative implementations of dependency injection.
For this reason, the examples report two ways to achieve certain things.
Examples
For examples, refer to the examples folder.
Recommended practices
All services should be configured once, when an application starts, and the
object graph should not be altered during normal program execution.
Example: if you build a web application, configure the object graph when
bootstrapping the application, avoid altering the Container
configuration
while handling web requests.
Aim at keeping the Container
and service graphs abstracted from the front-end
layer of your application, and avoid mixing runtime values with container
configuration. Example: if you build a web application, avoid if possible
relying on the HTTP Request object being a service registered in your container.
Service life style:
- singleton - instantiated only once per service provider
- transient - services are instantiated every time they are required
- scoped - instantiated only once per root service resolution call (e.g. once per web request)
Usage in BlackSheep
neoteroi-di
is used in the second version of BlackSheep
web framework to implement dependency injection for
request handlers.
Documentation
Under construction. 🚧
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