syringe module¶

A simple dependency injection library.

Usage¶

First decorate a class with @provides('a lookup name').

>>> import syringe
>>>
>>> @syringe.provides('cure')
... class Syrup:
...     def drink(self, person):
...         print('Nom nom')
...         person.health = 100
...

Instantiate it. Note that it is not possible to instanciate another instance of a class decorated with the name cure.

>>> syrup = Syrup()

Next inject it in another class using inject('a lookup name').

>>> class Person:
...     cure = syringe.inject('cure')
...
...     def drink_medicine(self):
...         self.cure.drink(self)
...

When an instance of the Person class is created, the value of the injecte name is the instance of the provided and instantiated class.

>>> person = Person()
>>> person.health = 20
>>> assert person.cure == syrup
>>> person.drink_medicine()
Nom nom
>>> assert person.health == 100

Mocking¶

A mock instance can be inserted using syringe.mock('a lookup name')

>>> try:
...     from unittest import mock
... except:
...     import mock
...
>>> m = syringe.mock('cure')
>>> person.drink_medicine()
>>> m.drink.assert_called_once_with(person)

syringe.clear()¶

Clears all current providers.

This may be useful for testing.

exception syringe.DuplicateProviderError¶

Bases: exceptions.ValueError

Raised when two providers for the same name have been instantiated.

syringe.get(name)¶

Returns the provided instance.

Parameters:	name (str) – The lookup name.
Returns:	The provided instance.

class syringe.inject(name)¶

Bases: object

Injects the instance of a provided class to the current context.

syringe.mock(name, m=None)¶

Provide a mock overriding any namespace conflicts.

If a second argument is passed, it is provided using the specified name. Otherwise a new unittest.mock.Mock instance is provided.

Parameters:	name (str) – The name of the mock to provide. m – The optional object to provide as a mock.

syringe.provides(name)¶

Provides the decorated class as an injectable object.

The class __init__ method is monkey patched so a DuplicateProviderError is raised when another instance is created for this name.

Parameters:	name (str) – The name under which the provided class will be accessible.

exception syringe.NoCandidateError¶

Bases: exceptions.KeyError

Raised when no candidate has been registered for the requested name.