DIpy

Introduction

DIpy is a simple, pure-python inversion of control container whose design is heavily inspired by Autofac.

DIpy features:

1. Flexible component resolution and registration.
2. Simple component lifetime management.
3. Higher-order component resolution.
4. Ability to stub missing dependencies.

Just to be clear, I don't think python needs a DI framework, nor do I think you should really use this. It is more of a curiosity.

Usage

The IOC container is provided by the Container class:

con = dipy.Container()

Components are identified by a string name and registered directly against a container instance:

con.register("widget", SimpleWidget)

Components can then be resolved from the container:

widget = con.resolve("widget")

When a component is registered via a type, resolving that component always returns a new instance:

widget1 = con.resolve("widget")
widget2 = con.resolve("widget")

return widget1 is widget2 # returns False

Dependencies are injected based on constructor parameters:

class ComplexWidget(object):
	def __init__(self, simple_widget)
		self.simple_widget = simple_widget

con = dipy.Container()

con.register("complex_widget", ComplexWidget)
con.register("simple_widget", SimpleWidget)

 # widget.simple_widget will be a new instance of SimpleWidget
widget = con.resolve("complex_widget")

An instance of a class may be registered directly. Each time that component is resolved, the same instance will be returned:

con.register("widget", SimpleWidget())

widget1 = con.resolve("widget")
widget2 = con.resolve("widget")

return widget1 is widget2 # returns True

It is also possible to indicate that only single instance of a component should be created per container:

con.register("widget", SimpleWidget, single_instance=True)

widget1 = con.resolve("widget")
widget2 = con.resolve("widget")

return widget1 is widget2 # returns True

Components can request higher-order dependencies that are derived based on dependency names. Appending "_list" to the end of a component name will inject a list of all components with that name:

class Machine(object):
	def __init__(self, widget_list):
		self.widgets = widget_list

con = dipy.Container()
con.register("widget", BlueWidget)
con.register("widget", GoldWidget)
con.register("widget", RedWidget)
con.register("machine", Machine)

# machine.widgets will contain a list of 3 elements, one for each widget type
machine = con.resolve("machine")

Adding "_fact" to a dependency name will inject a factory function that can be used to create instances of that dependency at runtime. Additional parameters required by the dependency can be passed to this function.

class ReportGenerator(object):
	def __init__(self, session_fact):
		self.session_fact = session_fact

	def do_it(self):
		sess = self.session_fact()
		sess.do_some_work()

DIpy provides simple lifetime management of all registered components. When a component is resolved, its __enter__ method is called, if applicable. When the container's __exit__ method is called, __exit__ is likewise called for all components that apply.

Finally, DIpy encourages proper unit testing of components by providing a built-in means of stubing components that have not been registered with the container:

class UserControl:
	def __init__(self, third_party_component_x):
		self.component = third_party_component_x

con = dipy.Container(autostub=True)
con.register("control", UserControl)

# control.component will be an instance of dipy.Stub
control = con.resolve("control")