slots-factory 0.1.2

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slot_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)

slots_from_type is a convenience function; you can also instantiate your own instance and then pass it through the underlying _slots_factory_setattrs function, which is what actually populates the attributes.

from slots_factory import type_factory
from slots_factory.tools.SlotsFactoryTools import _slots_factory_setattrs

my_type = type_factory(['x', 'y', 'z'], _name="SlotsObject")
instance = my_type()
_slots_factory_setattrs(my_type, {'x': 1, 'y': 2, 'z': 3})

@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)
307 ns ± 7.07 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()
275 ns ± 7.07 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]: [1, 2, 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]: [1, 3, 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}