IoC container module for Python with simple programming and configuration interface.

Declare enables implementation of extension-point/plugin in Python applications.

• Simple configuration file with JSON
• Specification of init parameters in configuration
• Support of component/object reference by identifier for init parameters
• Resolve components/objects by identifier
• Resolve components/objects by type, including class type and base types
• Singleton support

Sample configuration file:

{
	"resources" :
	{
		"RepeatableTaskRepeat": true
	},
	"component_specifications":
	{
		"AddWordDefinitionTask": {
			"class": "AddWordDefinitionTask",
			"module": "StandardDictionaryUserTasks",
			"initArgs": ["{$RepeatableTaskRepeat}"]
		},
		"ListWordDefinitionsTask":
		{
			"class": "ListWordDefinitionsTask",
			"module": "StandardDictionaryUserTasks",
			"lifetime": "singleton"
		},
		"RemoveWordDefinitionTask":
		{
			"class": "RemoveWordDefinitionTask",
			"module": "StandardDictionaryUserTasks",
			"initArgs": 
			{
				"repeat": "{$RepeatableTaskRepeat}"
			}
		}
	}
}

The sample above declared three components:

• AddWordDefinitionTask is of type AddWordDefinitionTask that can be found in StandardDictionaryUserTasks module. This component will be initialized with one argument True.
• ListWordDefinitionsTask is of type ListWordDefinitionTask that can be found in StandardDictionaryUserTasks module and it is also a singleton.
• RemoveWordDefinitionTask is a singleton component of of type RemoveWordDefinitionTask that can be found in StandardDictionaryUserTasks module. This component will be initialized with one named argument.

Objects declared in the configuration file can be resolved through an instance of Manager object which can be instantiated by passing an instance of Configuration object as follow:

import Declare

configuration = Declare.Configuration.Read(pathToJsonFile)
manager = Declare.Manager(configuration)

To resolve components of a type or components that inherits/implement a type :

components = manager.get_components_of_type(type=UserTask, lifetime="all")

The get_components_of_type function returns a list of objects that are either instance of or instance of a type that inherits/implements specified type. This function takes two arguments:

• type : type of class or base class
• lifetime : optional component lifetime filter. This argument defaults to "all". Other options include "singleton" and ""

To obtain a component by its identifier:

component = manager.get_component(identifier="RemoveWordDefinitionTask")

The get_component function accepts an identifier of an object as declared in the configuration file and return an object or None if the identifier is not found.