xeno 1.8.1

The Python dependency injector from outer space.

Pachimari, unofficial xeno mascot

Xeno: The Python dependency injector from outer space.

Xeno is a simple Python dependency injection framework. Use it when you need to manage complex inter-object dependencies in a clean way. For the merits of dependency injection and IOC, see https://en.wikipedia.org/wiki/Dependency_injection.

Xeno should feel pretty familiar to users of Google Guice in Java, as it is somewhat similar, although it is less focused on type names and more on named resources and parameter injection.

Installation

Installation is simple. With python3-pip, do the following:

$ sudo pip install -e .

Or, to install the latest version available on PyPI:

$ sudo pip install xeno

Usage

To use Xeno as a dependency injection framework, you need to create a xeno.Injector and provide it with modules. These modules are regular Python objects with methods marked with the @xeno.provider annotation. This annotation tells the Injector that this method provides a named resource, the same name as the method marked with @provider. These methods should either take no parameters (other than self), or take named parameters which refer to other resources by name, i.e. the providers can also be injected with other resources in order to build a dependency chain.

Once you have an Injector full of resources, you can use it to inject instances, functions, or methods with resources.

To create a new object instance by injecting resources into its constructor, use Injector.create(clazz), where clazz is the class which you would like to instantiate. The constructor of this class is called, and all named parameters in the constructor are treated as resource references. Once the object is instantiated, any methods marked with @inject are invoked with named resources provided.

Resources can be injected into normal functions, bound methods, or existing object instances via Injector.inject(obj). If the parameter is an object instance, it is scanned for methods marked with @inject and these methods are invoked with named resources provided.

Example

In this simple example, we inject an output stream into an object.

import sys
from xeno import *

class OutputStreamModule:
   @provide
   def output_stream(self):
      return sys.stdout

class VersionWriter:
   def __init__(self, output_stream):
      self.output_stream = output_stream

   def write_version(self):
      print('The python version is %s' % sys.version_info,
            file=self.output_stream)

injector = Injector(OutputStreamModule())
writer = injector.create(VersionWriter)
writer.write_version()

Checkout test.py in the git repo for more usage examples.

Change Log

Version 1.8: May 16th, 2017

• Add MissingResourceError and MissingDependencyError exception types.

Version 1.7: May 16th, 2017

• Major update, adding support for namespaces, aliases, and inline resource parameter aliases. See the unit tests in test.py for examples.

• Added @namespace('Name') decorator for modules to specify that all resources defined in the module should be scoped within ‘Name::’.

• Added @name('alt-name') to allow resources to be named something other than the name of the function that defines them.

• Added @alias('alt-name', 'name') to allow a resource to be renamed within either the scope of a single resource or a whole module.

• Added @using('NamespaceName') to allow the contents of the given namespace to be automatically aliases into either the scope of a single resource or a whole module.

• Added support for resource function annotations via PEP 3107 to allow inline aliases, e.g. def my_resource(name: 'Name::something-important'):

Version 1.6: April 26th, 2017

• Changed how xeno.MethodAttributes works: it now holds a map of attributes and provides methods get(), put(), and check()

Version 1.5: April 26th, 2017

• Added injection interceptors

• Refactored method tagging to use xeno.MethodAttributes instead of named object attributes to make attribute tagging more flexible and usable by the outside world, e.g. for the new injectors.

Version 1.4: August 30th, 2016

• Added cycle detection.

Version 1.3: August 29th, 2016

• Have the injector offer itself as a named resource named ‘injector’.