abstracts 0.0.5

Create an abstract.Abstraction

An Abstraction is a metaclass for defining abstract classes.

Let’s define an abstract AFoo class and give it an abstract do_foo method.

Like any python class, an Abstraction can have any name, but it may be helpful to distinguish abstract classes from others by prefixing their name with A.

>>> import abc
>>> import abstracts

>>> class AFoo(metaclass=abstracts.Abstraction):
...
...     @abc.abstractmethod
...     def do_foo(self):
...         raise NotImplementedError

Abstract classes cannot be instantiated directly.

>>> AFoo()
Traceback (most recent call last):
...
TypeError: Can't instantiate abstract class AFoo with abstract method... do_foo

Create an implementer for an abstract.Abstraction

In order to make use of AFoo, we need to create an implementer for it.

>>> @abstracts.implementer(AFoo)
... class Foo:
...     pass

The implementer must implement all of the abstract methods, defined by its abstract classes.

>>> Foo()
Traceback (most recent call last):
...
TypeError: Can't instantiate abstract class Foo with abstract method... do_foo

>>> @abstracts.implementer(AFoo)
... class Foo2:
...
...     def do_foo(self):
...         return "DID FOO"

>>> Foo2()
<__main__.Foo2 object at ...>

An implementer inherits from its Abstractions

An implementer class is a subclass of its Abstraction.

>>> issubclass(Foo2, AFoo)
True

Likewise an instance of an implementer is an instance of its Abstraction

>>> isinstance(Foo2(), AFoo)
True

The Abstraction class can be seen in the class bases, and the methods of the Abstraction can be invoked by the implementer.

>>> import inspect
>>> AFoo in inspect.getmro(Foo2)
True

Create an implementer that implements multiple Abstraction s.

An implementer can implement multiple abstractions.

Let’s create a second abstraction.

>>> class ABar(metaclass=abstracts.Abstraction):
...
...     @abc.abstractmethod
...     def do_bar(self):
...         raise NotImplementedError

And now we can create an implementer that implememts both the AFoo and ABar Abstraction s.

>>> @abstracts.implementer((AFoo, ABar))
... class FooBar:
...
...     def do_foo(self):
...         return "DID FOO"
...
...     def do_bar(self):
...         return "DID BAR"

>>> FooBar()
<__main__.FooBar object at ...>

Defining abstract properties

Properties can be defined in an abstract class, and just like with normal methods, they must be implemented by any implementers.

>>> class AMover(metaclass=abstracts.Abstraction):
...
...     @property
...     @abc.abstractmethod
...     def speed(self):
...         return 5
...
...     @property
...     @abc.abstractmethod
...     def direction(self):
...         return "forwards"