The Python dependency injector from outer space.
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 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
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
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
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
@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
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: @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()
test.py in the git repo for more usage examples.
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
SyncInjectorto allow injection to be performed in context of another event loop if async providers are not used.
AsyncInjectorto actually support asynchronous resolution of dependencies.
Version 4.1.0: Feb 3 2020
Injector.get_ordered_dependenciesto get a breadth first list of dependencies in the order they are built.
Version 4.0.0: May 12 2019
BACKWARDS INCOMPATIBLE CHANGE
- Removed support for parameter annotation aliases. Use
@aliason 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
BACKWARDS INCOMPATIBLE CHANGE
- 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
Injectornow 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
Injector.provide_async(). Note that resource are always run within an event loop and should not use
require()directly, instead they should use
require_async()to dynamically modify resources.
Version 2.4.1: January 30, 2018
Injector.scan_resources()to allow users to scan for resource names with the given attributes.
Attributes.merge()to assist with passing attributes down to functions which are wrapped in a decorator.
MethodAttributes.wraps()static decorator to summarize a common use case of attribute merging.
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
Version 2.3.0: January 21, 2018
- Added support for asyncio-based concurrency and async provider coroutines with per-injector event loops (
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
Version 2.0.0: July 25th, 2017
BACKWARDS INCOMPATIBLE CHANGE
- 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.
Version 1.9: May 23rd, 2017
@const()module annotation for value-based resources
Injector.get_dependency_tree()to fetch a tree of dependency names for a given resource name.
Version 1.8: May 16th, 2017
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.
@namespace('Name')decorator for modules to specify that all resources defined in the module should be scoped within 'Name::'.
@name('alt-name')to allow resources to be named something other than the name of the function that defines them.
@alias('alt-name', 'name')to allow a resource to be renamed within either the scope of a single resource or a whole module.
@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.MethodAttributesworks: it now holds a map of attributes and provides methods
Version 1.5: April 26th, 2017
- Added injection interceptors
- Refactored method tagging to use
xeno.MethodAttributesinstead 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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