Automatic "__slots__".
from autoslot import Slots
class Compact(Slots):
def __init__(self, a, b):
self.x = a
self.y = b
This produces exactly the same class as if you had done:
class Compact:
__slots__ = {'x', 'y'}
def __init__(self, a, b):
self.x = a
self.y = b
Simply: the code inside __init__()
is scanned to find all assignments to attributes on self
, and these are added as __slots__
.
The benefit of using autoslot.Slots
over a manual slots declaration is that you can modify the code inside the __init__()
method to add more attributes, and those changes will automatically be reflected in the __slots__
definition.
You can also have the best of both worlds: slots for fields you expect, as well as a __dict__
for those you don't:
from autoslot import SlotsPlusDict
class SemiCompact(SlotsPlusDict):
def __init__(self, a, b):
self.x = a
self.y = b
inst = SemiCompact(1, 2)
inst.z = 123 # <-- This won't fail!
Attributes x
and y
will be stored in slots, while all other dynamically-assigned attributes will go into the usual __dict__
instance inside the class. If most of your class's attributes appear in the __init__()
method (these will become slots), then the space bloat caused by dictionary hash-table expansion will be contained to only the dynamically-assigned attributes.
See for yourself! The code is tiny.
In words: the metaclass finds the __init__()
method, if present, and accesses its bytecode. It looks for all assignments to attributes of self
, and considers those to be desired __slots__
entries. Then the metaclass injects __slots__
into the namespace of the class definition and thereafter allows class creation to proceed as normal.
When __slots__
are used, weak references (e.g. using the weakref standard library module) won't work. If you need weak references, just set it up on a new __slots__
class variable as you would normally do without using autoslot
:
from autoslot import Slots
class Compact(Slots):
__slots__ = ['__weakref__']
def __init__(self, a, b):
self.x = a
self.y = b
Everything else will still work, and instances of Compact
will now also play nicely with the weakref module.