Library for building modular applications
A library for building modular applications.
pip install applipy
Applipy lets you:
- implement self-contained or interdependant
Modules that you can tell applipy to load for the application through the config file
AppHandles: instances that implement application lifecycle methods
- modules can register multiple
AppHandles that will be run concurrently
- load your application from a configuration file
- applipy will gracefully manage the lifecycle of your application
- define protocol handlers for a given URI scheme in configuration values. With these you can implement secrets that can be accessed by the application through the configuration.
An application can be defined by using a JSON (or YAML, if
# dev.yaml app: name: demo modules: - applipy_http.HttpModule - applipy_prometheus.PrometheusModule logging.level: DEBUG http.servers: - host: 0.0.0.0 port: 8080
Save a file
dev.yaml with the contents in the snipet above and run the
$ pip install pyyaml applipy applipy_http applipy_prometheus $ applipy
The configuration file above defines an application named
demo that installs
the applipy web module and the Prometheus module.
Applipy will search for a configuration file named
pyyaml is installed). The
default values are:
Another option is to indicate the file directly, using
applipy -f ./path/to/file.yaml.
AppHandle is the interface through wich applipy manages the lifecycle of the application. An AppHandle implementation looks like this:
# demo_app.py from asyncio import get_event_loop from logging import Logger from applipy import AppHandle class MyDemoApp(AppHandle): def __init__(self, logger: Logger, name: str): self.logger = logger.getChild(name) async def on_init(self): self.logger.info('initialize resources') self.future = get_event_loop().create_future() async def on_start(self): self.logger.info('run long lived application here') await self.future async def on_shutdown(self): self.logger.info('close and release resources') self.future.set_result(None)
As you can see above there is three methods exposed by AppHandles that let applipy run your application.
Applipy is capable of running multiple AppHandles concurrently, taking advantage of async in python.
The lifecycle of an application follow the following diagram:
Application.start() │ ▼ AppHandle.on_init() │ ▼ AppHandle.on_start() applipy cli │ SIGINT SIGTERM [Your own stopping mechanism] ▼ └────────┴───────┬───────────┘ start_long_running_task() ▼ │ Application.stop() ▼ │ AppHandle.on_shutdown()◄───────────────────────┘ │ ▼ wait(shutdown_timeout) │ ▼ cancel_all_tasks()
shutdown_timeout can be set in the app configuration using the key
app.shutdown_timeout_seconds. Defaults to 1 second.
It is expected that
AppHandle.on_shutdown()will be used to indicate any long running tasks to stop and cleanup, and do any required cleanup itself.
Generally, AppHandle implementations are added to the applipy application by
including the modules they are part of and registering the AppHandle in the
In applipy, modules are the building blocks of an application. They allow to
bind instances/classes/providers to types by exposing the an
bind() function, register application handles by exposing the Application's
register() function and define dependencies across modules.
An example of a module implementation looks like this:
# mymodule.py from applipy import Config, Module, LoggingModule from demo_app import MyDemoApp class MyModule(Module): def __init__(self, config: Config): self._config = config def configure(self, bind, register): bind(str, 'ModuleDemo') register(MyDemoApp) @classmethod def depends_on(cls): return (LoggingModule,)
The way you add modules to an application is through the configuration file by
defining a list of fully qualified names of Module implementations with
app: modules: - applipy_http.HttpModule - applipy_prometheus.PrometheusModule - mymodule.MyModule
Modules can only receive one parameter in their constructor and it is a
Config instance, as shown in the code above. If your module does not need
access to the configuration, you can just not implement a
__init__ or have it
not have arguments (other than
configure() method is run by the applipy
Application when it is started
and its purpose is to allow for binding types and registering application
handles. Check the extended
Module documentation in
depends_on() class method returns a tuple of the module types the
module depends on. In the example above, because the application handle
registered by the module requires a
logging.Logger, the module declares a dependency
LoggingModule because we know that it binds the
For a deeper dive on the features and details feel free to check the
subdirectory and the code itself!
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