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Unintrusive dependency injection for Python 3.6 +

Project description

Punq Documentation Status

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.


Punq is available on the cheese shop.

pip install punq

Documentation 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", "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):

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):

class ConsoleGreeter:
   def __init__(self, config_reader: ConfigReader):
      self.config = config_reader.get_config()

   def greet(self):


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):


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):

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.


0.2.1 2019-05-22


Punq will now prefer to use a provided resolution argument instead of creating it anew.

0.2.0 2019-02-12


Added handling for typing.ForwardRef

Breaking Changes

Added explicit instance kwarg to register which replaces the previous behaviour where container.register(Service, someInstance) would register a concrete instance. This fixes

0.1.2-alpha 2019-02-11


First automatic Travis deploy


Basic resolution and registration works Punq is almost certainly slow as a dog, non thread-safe, and prone to weird behaviour in the edge cases.

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