slots_factory
Factory functions and decorators for creating slot objects
Slots are a python construct that allows users to create an object that doesn't contain __dict__ or __weakref__ attributes. The benefit to a slots object is that it has faster attribute access and it saves on memory use, which make slots objects ideal for when you have lots of instances of a single python object.
I've never been a huge fan of the syntax though, as it requires repetitive code for definition as well as instantiation. yuck.
class SlotsObject:
__slots__ = ('x', 'y', 'z')
def __init__(self, x, y, z):
self.x = x
self.y = y
self.z = z
def __repr__(self):
contents = ", ".join(
[f"{key}={getattr(self, key)}" for key in self.__slots__]
)
return f"SlotsObject({contents})"
For funsies, I wanted to see if I could create a different way to instantiate these objects, with less jargon. Something like collections.namedtuple, but again without redundant definitions and with the benefits of __slots__. This repo is the results of such endeavor.
TL;DR - the @dataslots decorator ends up being the most useful implementation, free to skip to it if you want to see the fireworks.
slots_factory()
The first factory function made available is slots_factory. Simply import the function, and all **kwargs are assigned as attributes to an instance of a slots object. Type definitions are handled internally by the function, so successive calls to slots_factory with the same _name and **kwargs keys will return new instances of the same type.
For example:
In [1]: from slots_factory import slots_factory
In [2]: this = slots_factory(x=1, y=2, z=3)
In [3]: this
Out[3]: SlotsObject(x=1, y=2, z=3)
In [4]: that = slots_factory(x=4, y=5, z=6)
In [5]: that
Out[5]: SlotsObject(x=4, y=5, z=6)
In [6]: fizzbuzz = slots_factory(_name="fizzbuzz", fizz="fizz", buzz="buzz")
In [7]: fizzbuzz
Out[7]: fizzbuzz(fizz=fizz, buzz=buzz)
In [8]: slots_factory.__dict__
Out[8]:
{13844952821349480973: slots_factory.slots_factory.SlotsObject,
7572372383060875: slots_factory.slots_factory.fizzbuzz}
As we can see, we created three instances, this, that, and fizzbuzz. this and that are instances of the same type, since the function args were the same. fizzbuzz is a different type however, since its function arguments were different.
In [9]: type(this) == type(that)
Out[9]: True
In [10]: type(this) == type(fizzbuzz)
Out[10]: False
Another benefit to this SlotsObject is that, as the underlying type is a slots object, the attributes are dynamic, unlike the namedtuple.
In [11]: this.x = 4
In [12]: this
Out[12]: SlotsObject(x=4, y=2, z=3)
The type identification and attribute setting is all done in C, in attempt to make instantiation as fast as possible. Instantiation of a SlotObject is still about 80% slower than the instantiation of a namedtuple (mainly because it handles type definitions internally). Attribute access is on par however, and faster than a normal object as expected.
In [13]: from collections import namedtuple
In [14]: This = namedtuple('This', ['x', 'y', 'z'])
In [15]: %timeit this = This(x=1, y=2, z=3)
315 ns ± 1.58 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [16]: %timeit that = slots_factory('that', x=1,y=2,z=3)
597 ns ± 1.38 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [17]: %timeit this.c
24.6 ns ± 0.132 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
In [18]: %timeit that.c
25.8 ns ± 0.13 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
%time
fast_slots()
There's a second factory function, fast_slots, which is, obviously, faster. Instead of using the builtin hashing algorithm to generate an ID, it simply uses the object name and assumes that all objects named the same, are the same. Since it skips the hashing step, it builds slot instances much faster.
In [4]: from slots_factory import fast_slots
In [5]: %timeit that = fast_slots('that', x=1, y=2, z=3)
442 ns ± 3.71 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
Instead of relying on an internal ID mechanism, fast_slots leverages python's try/except functionality. The internal _slots_factory_setattrs method throws an exception when the object attributes are thought to be different, so when this happens fast_slots deletes its old internalized type definition and then builds a new one. As such, if you expect to be redefining the same type over and over again, it's best to use slots_factory for better overall performance. If however you're certain to be creating identical instances of the same type (with differing attribute variables of course, that is indeed allowed by fast_slots), then you'll be better of using fast_slots to do this.
from slots_factory import slots_factory, fast_slots
# use `slots_factory` like so:
this = slots_factory(x=1)
that = slots_factory(y=2)
# use `fast_slots` like so:
category = fast_slots('category', id=1, name='category 1')
category = fast_slots('category', id=2, name='category 2')
type_factory()
Finally, if we're really craving the speeds, the most efficient way to use this module is to individually define your types and then manually spin up instances of these objects. This can be done by importing the type_factory and slots_from_type functions.
from slots_factory import type_factory, slots_from_type
type_ = type_factory(['x', 'y', 'z'], _name="SlotsObject")
instance = slots_from_type(type_, x=1, y=2, z=3,)
In [6]: %timeit instance = slots_from_type(type_, x=1, y=2, z=3)
323 ns ± 10.4 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
@dataslots
There's a new decorator provided in the slots_factory module which attempts to improve upon Python's dataclasses.dataclass. Class definitions can be decorated with the @dataslots decorator to generate instances of analogous types with __slots__. I say analogous because at runtime the decorator instantiates a new type instead of modifying the user's defined type. The user's type is simply used as a sort of blueprint for generating the desired type with __slots__.
In [1]: from slots_factory import dataslots
@dataslots
class This:
x: int
y: int
z: int
In [2]: %timeit This(x=1, y=2, z=3)
397 ns ± 1.51 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
@dataslots
class This:
x: int = 1
y: int = 2
z: int = 3
In [2]: %timeit This()
261 ns ± 1.2 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
The @dataslots decorator allows for users to set default values using standard python syntax, and defaults can be overwritten simply by defining a new value at instantiation. There is no ordering restrictions on default definitions. It's also worth noting that, normally, when writing __slots__ classes, we can't define class attributes which conflict with the __slots__ structure that Python creates. However due to the internal mechanics of @dataslots, we can set __slots__ object defaults absent any annotations.
@dataslots
class FizzBuzz:
fizz = 'fizz'
buzz: str
fizzbuzz: str = 'spam'
In [5]: this = FizzBuzz(buzz='buzz', fizzbuzz='fizzbuzz')
Out[5]: FizzBuzz(fizz=fizz, buzz=buzz, fizzbuzz=fizzbuzz)
optional arguments for @dataslots
@dataslots provides a frozen keyword argument as a boolean. Passing frozen=True to the @dataslots decorator forces instances to be immutable.
@dataslots(frozen=True)
class FizzBuzz:
fizz: str = 'fizz'
buzz: str = 'buzz'
In [7]: fb = FizzBuzz()
In [8]: fb
Out[8]: FizzBuzz(fizz=fizz, buzz=buzz)
In [9]: fb.fizz = 'buzz'
-----------------------------------------------------------------------
AttributeError Traceback (most recent call last)
<ipython-input-9-63a20d67080e> in <module>
----> 1 fb.fizz = 'buzz'
~/programming/python/slots_factory/src/slots_factory/slots_factory.py in _frozen(self, *_, **__)
127 def _frozen(self, *_, **__):
128 raise AttributeError("instance is immutable.")
--> 129 methods.update({
130 "__setattr__": _frozen,
131 "__delattr__": _frozen
AttributeError: instance is immutable.
@dataslots also provides an order keyword argument as either a boolean or an iterable. If passed as a boolean, items are iterated over in whatever manner Python decides to sort the attribute names. Order can be made explicit by passing an iterable of attribute names for yielding.
@dataslots(order=True)
class This:
x: int
y: int
z: int
In [1]: this = This(x=1, y=2, z=3)
In [2]: [x for x in this]
Out[2]: [('x', 1), ('y', 2), ('z', 3)]
@dataslots(order=['x', 'z', 'y'])
class This:
x: int
y: int
z: int
In [3]: this = This(x=1, y=2, z=3)
In [4]: [x for x in this]
Out[4]: [('x', 1), ('z', 3), ('y', 2)]
Ordering implies hierarchy, and hierarchy provides a means for rich comparisons. Instances that are ordered can be compared using Python's builtin comparison operators. Comparison is done by applying the respected operator's method as defined on the self of the pair of objects, in order, across attributes. Comparison is resolved at first instance of inequality.
@dataslots(order=True)
class This:
x: int = 1
y: int = 2
z: int = 3
@dataslots(order=True)
class That:
x: int = 4
y: int = 5
z: int = 6
In [1]: this, that = This(), That()
In [2]: this < that
Out[2]: True
In [3]: this = This(x=6)
In [4]: this < that
Out[4]: False
Though dataslots are not dictionaries, they have many of the properties you would expect from a dictionary object. As such, conversion to and from dictionaries is built in. And as dictionaries are ordered in Python 3.6+, we make sure to preserve order between conversions.
@dataslots(order=["x", "z", "y"])
class This:
x: int
y: int
z: int
In [1]: this = This(x=1, y=2, z=3)
In [2]: that = dict(this)
In [3]: that
Out[3]: {'x': 1, 'z': 3, 'y': 2}
In [4]: dataslots.from_dict(that)
Out[4]: SlotsObject(x=1, z=3, y=2)
Dataslots also supports user-defined methods and properties. They can be defined as normal on the class, and @dataslots will be sure to carry these objects over to the __slots__ object.
@dataslots
class FizzBuzz:
fizz = 'fizz'
buzz: str = 'buzz'
def fizzbuzz(self):
return self.fizz + self.buzz
In [1]: fizzbuzz = FizzBuzz()
In [2]: fizzbuzz.fizzbuzz()
Out[2]: "fizzbuzz"
@dataslots
class FizzBuzz:
fizz = 'fizz'
buzz: str = 'buzz'
@property
def fizzbuzz(self):
return self.fizz + self.buzz
@fizzbuzz.setter
def fizzbuzz(self, item):
self.fizz, self.buzz = item
In [1]: fizzbuzz = FizzBuzz()
In [2]: fizzbuzz.fizzbuzz
Out[2]: 'fizzbuzz'
In [3]: fizzbuzz.fizzbuzz = ("This", "That")
In [4]: fizzbuzz.fizzbuzz
Out[4]: 'ThisThat'
Mutable default types in @dataslots via lambda
Given the nature of mutable types in Python, it's always been considered gauche to define default values as mutable types within object definitions. In order to allow for mutable defaults whose references aren't shared across instances, @dataslots default values can be assigned as either type type or a lambda expression with no arguments. These defaults are then called on instantiation, and instances assigned the result of the callable.
@dataslots
class RecordsCollection:
list_of_records = lambda: [{"record_id": 0, "name": "Terminal Record"}]
record_count: int = 1
def add_record(self, _id, name):
self.record_count += 1
self.list_of_records.append({
"record_id": _id,
"name": name
}
)
@dataslots
class RecordIds:
ids = set
def ingest_record(self, record):
for item in record.list_of_records:
self.ids.add(item["record_id"])
In [1]: n1 = RecordsCollection()
In [2]: %timeit RecordsCollection()
Out[2]: 496 ns ± 1.95 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)
In [3]: n2 = RecordsCollection()
In [4]: n1.add_record(5, "New Record")
In [5]: n1.list_of_records
Out[5]: [{'record_id': 0, 'name': 'Terminal Record'}, {'record_id': 5, 'name': 'New Record'}]
In [6]: n2.list_of_records
Out[6]: [{'record_id': 0, 'name': 'Terminal Record'}]
In [7]: rec_ids = RecordIds()
In [8]: rec_ids.ingest_record(n1)
In [9]: rec_ids.ids
Out[9]: {0, 5}
Inheritance and Composition in @dataslots
@dataslots objects can inherit artifacts from other dataslots. However, given that @dataslots is regenerating new datatypes on the fly, it currently doesn't have any concept of method resolution order, nor does it understand the concept of super(). A derived class simply updates its default values with preference given to the first base class in queue. Given this, class composition is generally regarded as a better implementation strategy, given @dataslots's compatibility with default type instantiations.
"""inheritance"""
@dataslots
class A:
a: list = lambda: [1,2,3]
@dataslots
class B:
a = list
@dataslots
class DerivedOne(A, B):
def get_list(self):
return self.a
@dataslots
class DerivedTwo(B, A):
def get_list(self):
return self.a
In [1]: instance_one = DerivedOne()
In [2]: instance_two = DerivedTwo()
In [3]: instance_one.get_list()
Out[3]: [1,2,3]
In [4]: instance_two.get_list()
Out[4]: []
"""composition"""
@dataslots
class SubcomponentOne:
x = 1
@dataslots
class SubcomponentTwo:
x = lambda: [1, 2, 3]
@dataslots
class RootClass:
s1 = SubcomponentOne
s2 = SubcomponentTwo
In [1]: instance = RootClass()
In [2]: repr(instance)
Out[2]: 'RootClass(s1=SubcomponentOne(x=1), s2=SubcomponentTwo(x=[1, 2, 3]))'
In [3]: instance.s2.x
Out[3]: [1, 2, 3]
Dependent defaults in @dataslots
Attributes oftentimes depend on the state of other attributes within an object. This can be tricky when it comes to default values in slots, as if you set values at type definition, those attributes become read-only. One solution to this is to define the attribute as a @property, so that the property has access to the instance when referenced.
@dataslots provides a leaner alternative, once again using the lambda function as a means for default assignments. lambda functions assigned to attributes can take a single argument, self. At instantiation the lambda is called and the resultant is assigned to the instance attribute.
import pymongo
import redis
from slots_factory import dataslots
@dataslots
class Redis:
queue = redis.Redis(host="redis-queue")
@dataslots
class Mongo:
client = pymongo.MongoClient("mongodb://mongo:27017")
database = lambda self: self.client.get_database("primary")
@dataslots
class Connections:
mongo = Mongo
redis = Redis
In [1]: conn = Connections()
In [2]: conn.mongo.database
Out[2]: Database(MongoClient(host=['mongo:27017'], document_class=dict, tz_aware=False, connect=True), 'primary')
Appendix: Some pure-Python implementations
This module uses custom C extensions for trying to speed up attribute write times. However the inclusion of this requires slots_factory to be installed and the extensions compiled. If that seems undesirable, here are some pure-Python implementations that can simply be copied into a codebase.
def slots_factory(_name="SlotsObject", **kwargs):
stores = slots_factory.__dict__
_keys = frozenset(kwargs)
if _name == "SlotsObject":
_id = hash(_keys)
_type = stores.get(_id)
else:
_id = hash(_name) ^ hash(_keys)
_type = stores.get(_id)
if not _type:
def __repr__(self):
contents = ", ".join(
[f"{key}={getattr(self, key)}" for key in self.__slots__]
)
return f"{self.__class__.__name__}({contents})"
_type = type(
_name,
(),
{"__slots__": _keys, "__repr__": __repr__}
)
stores[_id] = _type
instance = _type()
for key, value in kwargs.items():
setattr(instance, key, value)
return instance
def fast_slots(_name="SlotsObject", **kwargs):
_type = fast_slots.__dict__.get(_name)
if not _type:
def __repr__(self):
contents = ", ".join(
[f"{key}={getattr(self, key)}" for key in self.__slots__]
)
return f"{self.__class__.__name__}({contents})"
_type = type(
_name,
(),
{"__slots__": kwargs.keys(), "__repr__": __repr__}
)
fast_slots.__dict__[_name] = _type
instance = _type()
try:
for key, value in kwargs.items():
setattr(instance, key, value)
return instance
except AttributeError:
del fast_slots.__dict__[_name]
return fast_slots(_name, **kwargs)
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