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The Python dependency injector from outer space.

Project description

Xeno: The Python dependency injector from outer space.

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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

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 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


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.


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

import sys
from xeno import *

class OutputStreamModule:
   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,

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

Checkout in the git repo for more usage examples.

Change Log

Version 4.3.0: May 9 2020

  • Allow methods to be decorated with @injector.provide, eliminating the need for modules in some simple usage scenarios.

Version 4.2.0: May 8 2020

  • Split Injector into AsyncInjector and SyncInjector to allow injection to be performed in context of another event loop if async providers are not used.
  • Fixed AsyncInjector to actually support asynchronous resolution of dependencies.

Version 4.1.0: Feb 3 2020

  • Added Injector.get_ordered_dependencies to get a breadth first list of dependencies in the order they are built.

Version 4.0.0: May 12 2019


  • Removed support for parameter annotation aliases. Use @alias on methods instead. This was removed to allow Xeno code to play nicely with PEP 484 type hinting.

Version 3.1.0: August 29 2018

  • Add ClassAttributes.for_object convenience method

Version 3.0.0: May 4 2018


  • Provide injection interceptors with an alias map for the given param map.
  • This change breaks all existing injection interceptors until the new param is added.

Version 2.8.0: May 3 2018

  • Allow decorated/wrapped methods to be properly injected if their 'params' method attribute is carried forward.

Version 2.7.0: April 20 2018

  • The Injector now adds a 'resource-name' attribute to resource methods allowing the inspection of a resource's full canonical name at runtime.

Version 2.6.0: March 27 2018

  • Bugfix release: Remove support for implicit asynchronous resolution of dependencies. Providers can still be async, in order to await some other set of coroutines, but can no longer themselves be run in sync. The benefits do not outweigh the complexity of bugs and timing concerns introduced by this approach.

Version 2.5.0: March 2, 2018

  • Added Injector.provide_async(). Note that resource are always run within an event loop and should not use inject(), provide(), or require() directly, instead they should use inject_async(), provide_async(), and require_async() to dynamically modify resources.

Version 2.4.1: January 30, 2018

  • Added Injector.scan_resources() to allow users to scan for resource names with the given attributes.
  • Added Attributes.merge() to assist with passing attributes down to functions which are wrapped in a decorator.
  • Added MethodAttributes.wraps() static decorator to summarize a common use case of attribute merging.
  • Added MethodAttributes.add() as a simple static decorator to add attribute values to a method's attributes.

Version 2.4.0: January 21, 2018

  • Dropped support for deprecated Namespace.enumerate() in favor of Namespace.get_leaves().

Version 2.3.0: January 21, 2018

  • Added support for asyncio-based concurrency and async provider coroutines with per-injector event loops (injector.loop).

Version 2.2.0: September 19, 2017

  • Expose the Injector's Namespace object via Injector.get_namespace(). This is useful for users who want to list the contents of namespaces.

Version 2.1.0: August 23rd, 2017

  • Allow multiple resource names to be provided to Injector.get_dependency_graph().

Version 2.0.0: July 25th, 2017


  • Change the default namespace separator and breakout symbol to '/'

Code using the old namespace separator can be made to work by overriding the value of xeno.Namespace.SEP:

import xeno
xeno.Namespace.SEP = '::'

Version 1.10: July 25th, 2017

  • Allow names prefixed with :: to escape their module's namespace, e.g. ::top_level_item

Version 1.9: May 23rd, 2017

  • Add @const() module annotation for value-based resources
  • Add Injector.get_dependency_tree() to fetch a tree of dependency names for a given resource name.

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 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'.

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