Knot

Knot is a small do-it-yourself (DIY) dependency container for Python.

Getting started

Unlike other existing implementations, knot does not make use of introspection. Therefore, dependencies are manually defined in a straight forward manner. The container acts as a central registry for providers and configuration settings.

Configuration settings

The container is just an ordinary dictionary with some additional methods. As a result, it is very easy to assign or retrieve data from it. Probably the most common way to assign configuration settings is passing a dict to the constructor.

from knot import Container

c = Container({'host': 'localhost', 'port': 6379})

Obviously it is also possible to add configuration settings to an existing container.

c = Container()
c['host'] = 'localhost'
c['port'] = 6379

Providers

A provider creates and returns a particular value or object. It has the ability to utilize an injected container to retrieve the necessary configuration settings and dependencies.

The container expects a provider to adhere to the following rules:

1. It must be callable.
2. It must accept the container as the only argument.
3. It must return anything except None.

Assigning a provider to a container is easy.

def connection(c):
    from redis import Redis
    return Redis(host=c['host'], port=c['port'])

c.add_provider(connection, True)

It is also possible to use a decorator.

from knot import provider

@provider(c, True)
def connection(c):
    from redis import Redis
    return Redis(host=c['host'], port=c['port'])

The second argument in c.add_provider(connection, True) and in @provider(c, True) indicates whether or not the return value of a provider must be cached.

Retrieve what you have defined.

conn = c.provide('connection')

For convenience, you can also use the shortcut.

conn = c('connection')

Services

A service is just a provider with the cache argument set to True. Basically this means the return value is created only once.

def connection(c):
    from redis import Redis
    return Redis(host=c['host'], port=c['port'])

c.add_service(connection)

Or with a decorator.

from knot import service

@service(c)
def connection(c):
    from redis import Redis
    return Redis(host=c['host'], port=c['port'])

conn1 = c('connection')
conn2 = c('connection')

print conn1 is conn2 # True

Factories

A factory is just a provider with the cache argument set to False. Basically this means the return value is created on every call.

def urgent_job(c):
    from somewhere import Job
    connection = c('connection')
    return Job(connection=connection, queue='urgent')

c.add_factory(urgent_job)

job1 = c('urgent_job')
job1.enqueue('send_activation_mail', username='johndoe')

job2 = c('urgent_job')
job2.enqueue('send_activation_mail', username='janedoe')

print job1 is job2 # False

Or with a decorator.

from knot import @factory

@factory(c)
def urgent_job(c):
    from somewhere import Job
    connection = c('connection')
    return Job(connection=connection, queue='urgent')

Installation

Install Knot with the following command:

$ pip install knot

Tests

To run the tests, install pytest first:

$ pip install pytest

Then, run the tests with the following command:

$ make test

Inspiration

Pimple (http://pimple.sensiolabs.org/)

License

MIT, see LICENSE for more details.