Accessing dependencies

Antidote works with a Catalog which is a sort of collection of dependencies. Multiple ones can co-exist, but world is used by default. The most common form of a dependency is an instance of a given class

from antidote import injectable

@injectable
class Service:
    pass

world[Service]  # retrieve the instance
world.get(Service, default='something')  # similar to a dict

By default, @injectable defines a singleton but alternative lifetimes (how long the world keeps value alive in its cache) exists such as transient where nothing is cached at all. Dependencies can also be injected into a function/method with @inject. With both, Mypy, Pyright and PyCharm will infer the correct types.

from antidote import inject

@inject  #                      ⯆ Infers the dependency from the type hint
def f(service: Service = inject.me()) -> Service:
    return service

f()  # service injected
f(Service())  # useful for testing: no injection, argument is used

@inject supports a variety of ways to bind arguments to their dependencies if any. This binding is always explicit. for example:

from antidote import InjectMe

# recommended with inject.me() for best static-typing experience
@inject
def f2(service = inject[Service]):
    ...

@inject(kwargs={'service': Service})
def f3(service):
    ...

@inject
def f4(service: InjectMe[Service]):
    ...

Classes can also be fully wired, all methods injected, easily with @wire. It is also possible to inject the first argument, commonly named self, of a method with an instance of a class:

@injectable
class Dummy:
    @inject.method
    def method(self) -> 'Dummy':
        return self

# behaves like a class method
assert Dummy.method() is world[Dummy]

# useful for testing: when accessed trough an instance, no injection
dummy = Dummy()
assert dummy.method() is dummy

Defining dependencies

Antidote provides out of the box 4 kinds of dependencies:

• @injectable classes for which an instance is provided.

  from antidote import injectable
  
  #           ⯆ optional: would just call Service() otherwise.
  @injectable(factory_method='load')
  class Service:
      @classmethod
      def load(cls) -> 'Service':
          return cls()
  
  world[Service]

• const for defining simple constants.

  from antidote import const
  
  # Used as namespace
  class Conf:
      TMP_DIR = const('/tmp')
  
      # From environment variables, lazily retrieved
      LOCATION = const.env("PWD")
      USER = const.env()  # uses the name of the variable
      PORT = const.env(convert=int)  # convert the environment variable to a given type
      UNKNOWN = const.env(default='unknown')
  
  world[Conf.TMP_DIR]
  
  @inject
  def f(tmp_dir: str = inject[Conf.TMP_DIR]):
      ...

• @lazy function calls (taking into account arguments) used for (stateful-)factories, parameterized dependencies, complex constants, etc.

  from dataclasses import dataclass
  
  from antidote import lazy
  
  @dataclass
  class Template:
      name: str
  
  # the wrapped template function is only executed when accessed through world/@inject
  @lazy
  def template(name: str) -> Template:
      return Template(name=name)
  
  # By default a singleton, so it always returns the same instance of Template
  world[template(name="main")]
  
  @inject
  def f(main_template: Template = inject[template(name="main")]):
      ...

  @lazy will automatically apply @inject and can also be a value, property or even a method similarly to @inject.method.

• @interface for a function, class or even @lazy function call for which one or multiple implementations can be provided.

  from antidote import interface, implements
  
  @interface
  class Task:
      pass
  
  @implements(Task)
  class CustomTask(Task):
      pass
  
  world[Task]  # instance of CustomTask

  The interface does not need to be a class. It can also be a Protocol, a function or a @lazy function call!

  @interface
  def callback(event: str) -> bool:
      ...
  
  @implements(callback)
  def on_event(event: str) -> bool:
      # do stuff
      return True
  
  # returns the on_event function
  assert world[callback] is on_event

  @implements will enforce as much as possible that the interface is correctly implemented. Multiple implementations can also be retrieved. Conditions, filters on metadata and weighting implementation are all supported to allow full customization of which implementation should be retrieved in which use case.

Each of those have several knobs to adapt them to your needs which are presented in the documentation.

Testing & Debugging

Injected functions can typically be tested by passing arguments explicitly but it’s not always enough. Antidote provides test context which full isolate themselves and allow overriding any dependencies:

original = world[Service]
with world.test.clone() as overrides:
    # dependency value is different, but it's still a singleton Service instance
    assert world[Service] is not original

    # override examples
    overrides[Service] = 'x'
    assert world[Service] == 'x'

    del overrides[Service]
    assert world.get(Service) is None

    @overrides.factory(Service)
    def build_service() -> object:
        return 'z'


    # Test context can be nested and it wouldn't impact the current test context
    with world.test.clone() as nested_overrides:
        ...

# Outside the test context, nothing changed.
assert world[Service] is original

Antidote also provides introspection capabilities with world.debug which returns a nicely formatted tree to show what Antidote actually sees without executing anything like the following:

🟉 <lazy> f()
└── ∅ Service
    └── Service.__init__
        └── 🟉 <const> Conf.HOST

 ∅ = transient
 ↻ = bound
 🟉 = singleton

Going Further

• Scopes are supported. Defining a ScopeGlobalVar and using it as dependency will force any dependents to be updated whenever it changes (a request for example).

• Multiple catalogs can be used which allow you to expose only a subset of your API (dependencies) to your consumer within a catalog.

• You can easily define your kind of dependencies with proper typing from both world and inject. @injectable, @lazy, inject.me() etc.. all rely on Antidote’s core (Provider, Dependency, etc.) which is part of public API.

Check out the Guide which goes more in depth or the Reference for specific features.