Punq
An unintrusive library for dependency injection in modern Python. Inspired by Funq, Punq is a dependency injection library you can understand.
- No global state
- No decorators
- No weird syntax applied to arguments
- Small and simple code base with 100% test coverage and developer-friendly comments.
Installation
Punq is available on the cheese shop.
pip install punqDocumentation is available on Read the docs.
Quick Start
Punq avoids global state, so you must explicitly create a container in the entrypoint of your application:
import punq
container = punq.Container()Once you have a container, you can register your application's dependencies. In the simplest case, we can register any arbitrary object with some key:
container.register("connection_string", instance="postgresql://...")We can then request that object back from the container:
conn_str = container.resolve("connection_string")Usually, though, we want to register some object that implements a useful service.:
class ConfigReader:
def get_config(self):
pass
class EnvironmentConfigReader(ConfigReader):
def get_config(self):
return {
"logging": {
"level": os.env.get("LOGGING_LEVEL", "debug")
},
"greeting": os.env.get("GREETING", "Hello world")
}
container.register(ConfigReader, EnvironmentConfigReader)Now we can resolve the ConfigReader service, and receive a concrete implementation:
config = container.resolve(ConfigReader).get_config()If our application's dependencies have their own dependencies, Punq will inject those, too:
class Greeter:
def greet(self):
pass
class ConsoleGreeter(Greeter):
def __init__(self, config_reader: ConfigReader):
self.config = config_reader.get_config()
def greet(self):
print(self.config['greeting'])
container.register(Greeter, ConsoleGreeter)
container.resolve(Greeter).greet()If you just want to resolve an object without having any base class, that's okay:
class Greeter:
def __init__(self, config_reader: ConfigReader):
self.config = config_reader.get_config()
def greet(self):
print(self.config['greeting'])
container.register(Greeter)
container.resolve(Greeter).greet()And if you need to have a singleton object for some reason, we can tell punq to register a specific instance of an object:
class FileWritingGreeter:
def __init__(self, path, greeting):
self.path = path
self.message = greeting
self.file = open(self.path, 'w')
def greet(self):
self.file.write(self.message)
one_true_greeter = FileWritingGreeter("/tmp/greetings", "Hello world")
container.register(Greeter, instance=one_true_greeter)You might not know all of your arguments at registration time, but you can provide them later:
container.register(Greeter, FileWritingGreeter)
greeter = container.resolve(Greeter, path="/tmp/foo", greeting="Hello world")Conversely, you might want to provide arguments at registration time, without adding them to the container:
container.register(Greeter, FileWritingGreeter, path="/tmp/foo", greeting="Hello world")Fuller documentation is available on Read the docs.
Github workflows, nox configuration, and linting gratefully stolen from Hypermodern Python