Autoinject

A clean, simple framework for automatically injecting dependencies into objects and functions based around Python's type-hinting system. The framework provides caching of injectable objects, though this may be disabled on a class-by-class basis. It also supports managing independent caches for different contexts.

Define Injectable Classes

# Easy mode

from autoinject import injector

@injector.injectable
class MyInjectableClass:

    # __init__() should have no additional required arguments
    def __init__(self):
        pass


# Hard mode, must specify the fully-qualified name of the class,
# but gain control over the arguments

@injector.register("example.MyInjectableClass", os.environ("MY_CONFIG_FILE"))
class MyInjectableClass:

    def __init__(self, config_file):
        # we receive os.environ("MY_CONFIG_FILE") as config_file here
        # positional and keyword arguments to @injector.register() are supported
        pass

Inject Objects With Decorators

# Decorate with @injector.inject for functions/methods:

@injector.inject
def inject_me(param1, param2, injected_param: MyInjectableClass):
    # injected_param is set to an instance of MyInjectableClass
    pass

# Omit the injected parameters when calling it:

inject_me("arg1", "arg2")


# For classes, use @injector.construct to set instance attributes 
# based on the class attributes   
class InjectMe:

    injected_attribute: MyInjectableClass = None

    @injector.construct
    def __init__(self):
        # self.injected_attribute is set to an instance of MyInjectableClass
        pass

# No need to do anything special here:
obj = InjectMe()
# obj.injected_attribute is set by the decorator before __init__() is called.

Specifying injected classes in tests

You can override injected classes in your unit tests using the @injector.test_case() decorator. This provides an independent global context within the test case function and allows you to pass a map of objects to inject. For example,

from autoinject import injector 

# Your injectable original class
@injector.injectable_global 
class ServiceConnection:
  
  def execute(self) -> int:
    # Real connection code here, returns HTTP status code
    pass
  

# The class you want to write a test case for that uses the injectable class.
class UsesServiceConnection:
  
  connection: ServiceConnection = None
  
  @injector.construct 
  def __init__(self):
    pass
  
  def test_me(self) -> bool:
    # Super simple, check if response code is under 400
    resp_code = self.connection.execute()
    return resp_code < 400
  
  
# Testing stuff
import unittest
  
# Stub for testing
class _StubServiceFixture:
  
  def __init__(self, response_code):
    self.response_code = response_code
  
  def execute(self) -> int:
    return self.response_code


# Test case
class TestUsesServiceConnection(unittest.TestCase):

    @injector.test_case({
      ServiceConnection: _StubServiceFixture(200)
    })
    def test_success_200(self):
        test_obj = UsesServiceConnection()  # this will use the injected objects now
        self.assertTrue(test_obj.test_me())


    @injector.test_case({
      ServiceConnection: _StubServiceFixture(400)
    })
    def test_failure_400(self):
        test_obj = UsesServiceConnection() 
        self.assertFalse(test_obj.test_me())

Read the full documentation for more details.

Changelog

v1.3.3

• Member lists of objects are now cached to prevent multiple calls to inspect.getmembers() when the same class is created many times. This results in significant speed increases.

v1.3.0

• The new @injector.test_case() decorator is available for use with unit testing frameworks. It executes the decorated function with a different global and non-global context to ensure the independence of test functions. In addition, one can override the injected classes to provide specific test fixtures. These are passed as a dict of either type objects or fully qualified class names as strings as keys and either the type or class name as string (to create the object), or an object or function to use as the injected object.
• A bug was fixed where exceptions within a context caused issues with the new contextvars integration.

v1.2.0

• Contextvar-driven contexts are now respected by default
• Several wrappers exist to better support using contextvars. All of them provide for a separate set of injected CONTEXT_CACHE dependencies. In addition, each is a wrapper around @injector.inject, so both are not needed.
  • @injector.with_contextvars: Creates a new context that is a copy of the current one
  • @injector.with_same_contextvars: Uses the current context
  • @injector.with_empty_contextvars: Creates a new empty context
• When using a with_contextvars wrapper, you can inject the context object using type-hinting (e.g. ctx: contextvars.Context). Note that this is actually an instance of ContextVarsManager which is a context manager that delegates most functionality to the current contextvars.Context object with a few modifications:
  • It provides the method set(context_var, value) -> token and the complementary reset(context_var, token) to handle variable setting and resetting within the context manager.
    • If the "same" context is used, these methods are equivalent to calling the methods directly on the context_var
    • In all other cases, they are equivalent to calling ctx.run(context_var.METHOD, *args, **kwargs).
    • In essence, this makes sure the set() and reset() operations are performed in the context that the manager is managing (since the manager doesn't run the inner block in the context).
  • If the "same" context is used:
    • run() will just directly call the function (it is in the current context essentially)
    • copy() is an alias for contextvars.copy_context()
    • Other functions besides set() and reset() make a copy of the current context and return the results of its method. This copy is transient and remade each time, so modules making extensive use of it can call copy() and check the copy.
• Note that, unlike the context manager, the decorators also RUN the inner code in the given context.
• Thread-handling was improved significantly and now also includes a wrapper function for threading.Thread.run() methods to ensure clean-up (@injector.as_thread_run()). This also is a wrapper around @injector.inject so you can inject variables into your run() method directly.

v1.1.0

• Injectable objects may now define a __cleanup__() method which will be invoked when the global cache or context cache is cleared.
• Note that __cleanup__() IS NOT INVOKED for one-time use objects at the moment, but this is planned as a feature.

v1.0.1

• Inherited injectable class members are now supported properly

v1.0.0

• Official initial release
• Added support for @injector.injectable_global which registers with GLOBAL cache instead of context-specific cache
• Added support for @injector.injectable_nocache which registers with NO_CACHE instead
• Added support for injector.override() as a helper function to replace one constructor with another.
• Added support for any constructor argument (e.g. via override() or register_constructor()) to be specified by fully-qualified Python name (e.g. package.module.MyInjectableClass) to better support systems where injected classes are specified by name.
• Fixed a bug whereby the cache wasn't cleared

v0.2.2

• Fixed a bug for injection when a non-truthy default value needed to be used.

v0.2.1

• Fixed a bug in Python 3.8 and 3.9 where entry_points(group=?) was not supported

v0.2.0

• Objects with a cache strategy of CONTEXT_CACHE will now have separate instances within threads
• Added injector.get() as a fast way to get the object that would be injected (useful if operating outside of a function or method)
• Added injector.register_constructor() as a wrapper to register a class in a non-decorated fashion
• Added the entry point autoinject.injectables to directly register injectable classes
• Added the entry point autoinject.registrars
• Support for overriding injectables and for injecting functions
• Added a weight keyword argument to register() and register_construct() to control overriding order
• There is now a cleanup() function in the ContextManager() class which triggers informant objects to check for old items that are no longer needed. This was added mostly to support the thread-based context informant, since it has no easy way of calling destroy() whenever the thread ends (unless one manually calls it). It is the best practice if you can call destroy() directly whenever a context ceases to exist instead of relying on cleanup().