pymple 0.0.5

A simple Inversion of Control container

Why

If you search for Inversion of Control containers for Python you often encounter the argument “Python is dynamic and does not need those things that static languages need”. This is partly true.

Dependency Injection and Inversion of Control is a pattern and not a language feature. It not only makes your code easier to test, but also way more readable. The dependencies are clearly noted in the constructor and your IDEs will give you autocompletion support. If you need to test a class, it is clear where and how to pass in the mocks.

Therefore Inversion and Control and Dependency Injection (which go hand in hand) should also be practiced in dynamic languages. If you think this is not viable, check out AngularJS which also makes use of the above mentioned patterns in a dynamic programming language, namely JavaScript.

For further information watch Google’s Clean Code Talks

Limitations

Pymple does currently not support:

• Threadsafety

• Lifetimes

Installation

This library is a Python 3.2+ library.

Install it via pip for Python 3:

sudo pip3 install pymple

Usage

Pymple knows three types of parameters:

• Values: A value is simply value that is saved and reused for all other factories/singletons

• Singletons: A singleton is a callable that is executed once and the result is saved so future calls to the build method will return the same instance

• Factories: A factory is callable that is executed again everytime it is accessed

Registering a value

from pymple import Container

container = Container()
container.value('my_int', 2)

container.build('my_int') == 2 # True

Registering a Singleton

from pymple import Container

class MyClass:
    def __init__(self, value):
        self.value = value

container = Container()
container.value('my_int', 2)
container.singleton(MyClass, lambda x: MyClass(x.build('my_int')))

container.build(MyClass) == container.build(MyClass) # True
container.build(MyClass).value == 2 # True

Registering a Factory

from pymple import Container

class MyClass:
    def __init__(self, value):
        self.value = value

container = Container()
container.value('my_int', 2)
container.factory(MyClass, lambda x: MyClass(x.build('my_int')))

container.build(MyClass) == container.build(MyClass) # False
container.build(MyClass).value == 2 # True

Using the @inject decorator

Instead of registering all values in the container, you can try to let the container assemble the class automatically

from pymple import Container

class A:
    pass

container = Container()
    a = container.build(A)

    isinstance(a, A) # True

This works if the constructor is empty. If the constructor is not empty, the container needs a map from parameter value to container value as a static _inject attribute on the class. This attribute can be set with the @inject decorator:

from pymple import inject, Container
from some.module import A

@inject(value=A, value2='param')
class C:

    def __init__(self, value, value2):
        self.value = value
        self.value2 = value2

container = Container()
container.value('param', 3)
c = container.build(C)

isinstance(c.value, A) # True
c.value2 == 3 # True

Extending the container

You can also extend the container to make it reusable:

from pymple.container import Container

class MyContainer(Container):

    def __init(self):
        super().__init__()
        self.value('value', 3)
        # etc


container = Container()
container.build('value') == 3 # True