Package: epoxy
EpoxyIntroductionEpoxy is an inversion of control framework for Python applications
packaged with a set of adapters that can be used with a number of
existing technologies. Epoxy allows you to clearly separate out the
concern of mapping dependencies to components from defining those
components.Epoxy is probably overkill for small apps (like the example below) but
shows its true value on larger projects where a higher degree of
flexibility and lower degree of coupling is desirable.LicenseThis library is available under the terms of the MPL. Please see the
LICENSE file for details.An ExampleHere’s an example of an epoxy component:from epoxy.component import Component, Dependency

class PrinterComponent(Component):

    prefix = StringSetting(required=False, default="PRINTING")

    def print(self, stuff):
        print ("[%s] %%s" % self.prefix) % stuff

    def start(self):
        print self.print("Warming up printer")


class ScreenRenderer(Component):

    printer = Dependency()

    def render_screen(self):
        self.printer.print("My Stuff")

    def start(self):
        self.printer.print("Screen Renderer Initialized")In this example, ScreenRenderer does not need to know the precise
printer which will be used as a dependency at runtime, it just needs to
declare the dependency and use it (there is an assumed interface, as
with much in python we just use duck typing).To wire these components up at runtime, we would write a yaml file that
would have something like this:components:
  printer:
    class: my.module:PrinterComponent
    settings:
      prefix: PREFIX

  screen_renderer:
    class: my.module:ScreenRenderer
    dependencies:
      printer: printer

entry-point:
  screen_renderer:render_screenFinally, to load in our configuration and run the application, we would
write something like the following:from epoxy.configuration import YamlConfigurationLoader
from epoxy.core import ComponentManager

loader = YamlConfigurationLoader("myapp.yml")
config = loader.load_configuration()
component_mgr = ComponentManager()
component_mgr.launch_configuration(config)This would run our entry point and print the following to the screen:[PREFIX] Warming up printer
[PREFIX] Screen Renderer Initialized
[PREFIX] my stuffWriting a ComponentAny Component that is written should follow these basic rules in order
to play nicely:No-args constructor: Components should have a no-args constructor in
order to be instantiated by the framework. To initialize a Component
in your own code (maybe from a unit test) you can use the
“from_dependencies” classmethod available on any component and pass
in any relevant dependencies/settings as keyword arguments.For instance, instantiating our previous object graph would look like
the following:printer = PrinterComponent.from_dependencies(prefix="FROM_DEPS")
renderer = ScreenRenderer.from_dependencies(printer=printer)When__init__is executed it is guaranteed that all dependencies
will be present and initialized (but not started).Implementstart()method: After all objects in the graph are
instantiated, they will be started. Like with__init__,
dependencies will be present and will have hadstart()called.
Calls tostart()should not block. For long-running tasks, using
an entry-point is more appropriate.Avoid Dependency Cycles: If the object graph has dependencies, you
will get errors when trying to build the dependency graph and you
will not be able to run your application. There are many different
strategies for breaking these cycles. If you run into this issue and
are ticked off, just know that fixing this issue is making your
application better.