pythonioc 0.4.1
Simplistic dependency injection container for python
License: MIT

.. role:: bash(code)
    :language: bash

Simple Inversion-Of-Control-Container for python
================================================

This package provides a simple inversion-of-control container.

Install with 

.. code:: bash

    pip install pythonioc

Quick Start
-----------

The main idea is: services are registered to a service-registry and can be injected into users of that service (which can of course be services themselves).

You have two options: 

(A) use a global registry (never create a registry yourself)
    
(B) use a local registry
    
Examples are below, more details will follow.

Global Registry
^^^^^^^^^^^^^^^

.. code:: python

    import pythonioc

    # register your service with a default name (here: 'someService', see Notes On Names)
    @pythonioc.Service
    class SomeService(object):
    
        # called when the service is auto-instantiated.
        def postInit(self):
            pass
        
    @pythonioc.NamedService('DifferentNameService')
    class DifferentService(object):
        pass        
        
    # for classes which we cannot decorate:
    pythonioc.registerService(ExternalService)
    
    # when we don't even have the class (or don't care about lazy-initialization)
    pythonioc.registerServiceInstance(SomeService())
    
    
    class ServiceUser(object):
        # inject the dependency by class
        service = pythonioc.Inject(SomeService)
        
        # inject the dependency by name (for cyclic dependencies)
        service2 = pythonioc.Inject('DifferentNameService')
       
      
     myUser = ServiceUser()
     
     myUser.service # --> automatically created and injected service instance.
     
     # explicitly get a service
     pythonioc.getService(SomeService)
     pythonioc.getService('DifferentNameService')

     

Local Registry
^^^^^^^^^^^^^^

.. code:: python


    class Service(object):
        
        # this will make the service registry inject a service named "someOtherService" which 
        # comes from class SomeOtherService
        _someOtherService = None
        
        def __init__(self):
            pass
            
        # will be called after everything is injected
        def postInit(self):
            pass
            
        # will be called right before the object is destroyed (the registry's clean
        # method is called)
        def preDestroy(self):
            pass
            
            

    class SomeOtherService(object):
        pass
        
    # let's register our services
    reg = ServiceRegistry()
    reg.registerService(Service)
    reg.registerService(SomeOtherService)

Once everything is registered, a service can be injected by

.. code:: python


    class WiredUser(object):

        _service=None
        
        def __init__(self, *args):
            pass
            
    wiredUser = reg.createWired(WiredUser, 'arg1', 'arg2')

Wired objects are not automatically part of the service registry, only
if added by calling ``reg.registerServiceInstance``. 

Wired objects can inject their own service registry, so they can create wired objects on the fly:

.. code:: python


    class WiredUser(object):
        _service=None
        

    class UserCreator(object):
        _serviceRegistry=None
        
        def createUser(self):
            return self._serviceRegistry.createWired(WiredUser) 
        
    userCreator = reg.createWired(UserCreator)

    # create some wired users
    userA = userCreator.createUser()
    userB = userCreator.createUser()


Notes on Names
--------------

Services added to the registry need a name. If no name is provided, the class' name (or the instance's class name) is used. The name's first character is lowered by convention.

Example:

.. code:: python

    import pythonioc
    
    class MyService(object):
        pass
    
    pythonioc.registerService(MyService)            # --> name is 'myService'
    pythonioc.registerServiceInstance(MyService())  # --> name is 'myService'
    pythonioc.registerService(MyService, serviceName='customName') # --> name is 'customName'
    pythonioc.registerServiceInstance(MyService(), serviceName='customName2')  # --> name is 'customName2'
    

Notes on Dependency Cycles
--------------------------

Generally, dependency cycles are resolved by lazily initializing services. Critical cycles can still occur, when two services depend on each other within their `postInit`-methods that are executed after initialization. Those cycles are detected by keeping track of the currently running postInit methods and throwing an exception.

The service creation is thread safe, so accessing a non-initialized service with a long-running init or postInit method from two different threads will block one of the threads.


Bugs
----

Bug reports, suggestions for improvements etc. are always welcome!