slotted 4.2.1

Enforces usage of '__slots__' for python classes.

Overview

slotted enforces usage of __slots__ for Python classes.

Examples

When defining a Slotted class with no __slots__ declaration, it assumes it has empty slots, which is equivalent to declaring __slots__ = ().

>>> from slotted import Slotted

>>> class Foo(Slotted):
...     pass  # implicit declaration of __slots__ = ()
...
>>> foo = Foo()
>>> foo.bar = 1
Traceback (most recent call last):
AttributeError: 'Foo' object has no attribute 'bar'

Slotted classes can be mixed with regular classes as long as they and all of their bases implement __slots__.

>>> from slotted import Slotted

>>> class Bar:
...     __slots__ = ("bar",)
>>> class Foo(Bar, Slotted):
...     __slots__ = ("foo",)
...
>>> foo = Foo()

If any non-Slotted class anywhere in the chain does not implement __slots__, a TypeError exception is raised.

>>> from slotted import Slotted

>>> class Bar:
...     pass
>>> class Foo(Bar, Slotted):
...     __slots__ = ("foo",)
...
Traceback (most recent call last):
TypeError: base 'Bar' does not define __slots__

Slotted behavior can also be achieved by using the SlottedMeta metaclass.

>>> from six import with_metaclass
>>> from slotted import SlottedMeta

>>> class Foo(with_metaclass(SlottedMeta, object)):
...     pass  # implicit declaration of __slots__ = ()
...
>>> foo = Foo()
>>> foo.bar = 1
Traceback (most recent call last):
AttributeError: 'Foo' object has no attribute 'bar'

abc

slotted also provides generic versions of the collection.abc classes.

>>> from typing import TypeVar
>>> from slotted import SlottedMapping, SlottedSequence, SlottedSet
>>> KT = TypeVar("KT")
>>> VT = TypeVar("VT")
>>> class MyMapping(SlottedMapping[KT, VT]):
...     pass # implicit declaration of __slots__ = ()
...
>>> class MySequence(SlottedSequence[VT]):
...     pass # implicit declaration of __slots__ = ()
...
>>> class MySet(SlottedSet[VT]):
...     pass # implicit declaration of __slots__ = ()
...

For Python 2.7, slotted adds a SlottedCollection class, even though the original Collection is not available.

>>> from typing import TypeVar
>>> from slotted import SlottedCollection
>>> T = TypeVar("T")
>>> class MyCollection(SlottedCollection[T]):
...     pass # implicit declaration of __slots__ = ()
...