xeno 7.8.3

The Python IOC app and build framework from outer space.

xeno: The Python dependency injector from outer space.

xeno at its core 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.

xeno also offers xeno.build, a build automation framework built atop the core dependency injection inspired by Invoke. It is intended to come with batteries-included tools for making C/C++ projects, executing shell scripts, batching, and more. It is built on the concept of composable "recipes", which are generic instructions for building different types of filesystem targets.

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

As a build automation framework

To use xeno.build to build a simple C software project, first create a file called build.py in your repo (it can be called anything, but this is customary). Follow this template example for guidance:

#!/usr/bin/env python3
from xeno.build import *

# TODO: Add recipes, providers, and tasks here.

build()

Then, you can import the compile recipe from xeno.recipes.c:

from xeno.recipes.c import compile, ENV

ENV here is the default environment variables that compile will use by default. It defaults to using clang to compile C projects, you can change that here, and you can add additional compile-time flags. The ENV object is of type xeno.shell.Environment, which allows for some complex shlex-based joining and recombining of flags, such that you can additively compose the enviornment with defaults and/or what may be specified outside the build script. You can also provide your own environment variables via the env= parameter to compile.

ENV['CC'] = 'gcc'
ENV += dict(
    LDFLAGS='-g'
)

Let's create a provider that lists all of our source files and another that lists our headers. This will be useful for defining our tasks and using the compile recipe.

from pathlib import Path

@provide
def source_files():
    return Path.cwd().glob("src/*.c")

@provide
def header_files():
    return Path.cwd().glob("include/*.h")

Next, let's define a single default task that builds our program.

@task(default=True)
def executable(source_files, header_files):
    return compile(source_files, target="my_program", headers=header_files)

compile can take iterables of source files and/or combinations of strings and lists in *args. In this case, we elected to specify a target name for the program. If this wasn't the case, the name of the resulting target would be based on the name of the first source file. This is ideal if there is only one source being provided or if the main source file is always provided first and is the desired name of the executable, but in this case it would be whatever came first in the directory order which isn't deterministic or ideal.

Specifying the headers= parameter here links the recipe to our header files as static file dependencies. If these files change, the recipe is acknowledged to be outdated, and will be rebuilt the next time the build script is run even if an executable target already exists.

That's it! Let's put it all together, and then we'll have a build script for our program.

#!/usr/bin/env python3
from xeno.build import *
from xeno.recipes.c import compile, ENV
from pathlib import Path

ENV['CC'] = 'gcc'
ENV += dict(
    LDFLAGS='-g'
)

@provide
def source_files():
    return Path.cwd().glob("src/*.c")

@provide
def header_files():
    return Path.cwd().glob("include/*.h")

build()

Mark this script as executable and run it as ./build.py, or use python build.py. Be sure to check out ./build.py --help for a list of command line options and running modes. xeno.build is smart and can create addressable targets from a variety of different nested recipe construction scenarios, so build more complex scripts and try out ./build.py -L to see them all!

Watch this space for more in-depth documentation to come in the near future.

As an IOC framework

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 7.3.0: Oct 9 2023

• xeno.build targets can now receive arguments! All args after a lone '@' arg are packed into an implicit argv resource that can be injected into targets automatically.
• Fixed broken run_as functionality in ShellRecipe.

Version 7.2.2: Oct 7 2023

• Add a **kwargs pass-thru for xeno.shell.check() for passing args to subprocess.check_output().

Version 7.2.1: Sep 15 2023

• Allow recipe factories to return empty results as None (or no explicit return value).

Version 7.2.0: Sep 15 2023

• Improvements to the busy spinner: it now loops through pending recipe sigils to let the user know what is blocking in the build.
• Improved xeno.recipes.checkout() now opens build.py and checks its Python AST for references to "xeno" before trying to run "./build.py deps" if "build.py" is present in the resulting repository.

Version 7.1.0: Sep 09 2023

• Add a update() override to xeno.shell.Environment which takes the same arguments as select() but updates the dictionary in-place instead of making and returning a new one.

Version 7.0.0: Sep 09 2023

• Lift various build recipes from different projects into a "batteries-included" set of build tools under xeno.recipes.**.
• New enriched focus on backwards compatibility between minor versons.
• Restructuring and refactoring, xeno.cookbook is deprecated.
• From now on, legacy features will be marked as deprecated and made to continue to work until the next major version, during which they will be removed.

Version 4.12.0: Aug 07 2022

• Changes to support Python 3.10, older versions are now deprecated.

Version 4.10.0: Oct 28 2021

• Allow recipes to be specified with glob-style wildcards, as per fnmatch.

Version 4.9.0: Jan 03 2021

• Deprecate @recipe factory decorator for @factory.
• Allow recipes to specify a setup recipe, which is not part of the recipe inputs or outputs but is needed to fulfill the task.

Version 4.8.0: Dec 29 2020

• All recipe resources are loaded before targets are determined.
• Recipe names are now valid targets for a build.

Version 4.7.0: Dec 16 2020

• Fixed a bug where build would continue resolving with outdated results.
• Added @recipe decorator to xeno.build to denote recipe functions.

Version 4.4.0: Nov 2 2020

• Added experimental xeno.build module, a declarative build system driven by IOC.
• Added xeno.color offering basic ANSI color and terminal control.

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

BACKWARDS INCOMPATIBLE CHANGE

• 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

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

• 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

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. ::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 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'.