168. __slots__ for Memory EfficiencyPage 4

Snippet 1: Basic Usage of __slots__

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class Person:
    __slots__ = ('name', 'age')

    def __init__(self, name, age):
        self.name = name
        self.age = age

p = Person("Alice", 30)
print(p.name, p.age)
# p.address = "New York"  # AttributeError: 'Person' object has no attribute 'address'

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Snippet 2: Memory Comparison with and without __slots__

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import sys

class WithoutSlots:
    def __init__(self, name, age):
        self.name = name
        self.age = age

class WithSlots:
    __slots__ = ('name', 'age')

    def __init__(self, name, age):
        self.name = name
        self.age = age

obj1 = WithoutSlots("Alice", 30)
obj2 = WithSlots("Alice", 30)

print(sys.getsizeof(obj1.__dict__))  # Memory used without __slots__
print(sys.getsizeof(obj2))          # Memory used with __slots__

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Snippet 3: Preventing Dynamic Attribute Addition

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class FixedAttributes:
    __slots__ = ('a', 'b')

obj = FixedAttributes()
obj.a = 10
obj.b = 20
# obj.c = 30  # AttributeError: 'FixedAttributes' object has no attribute 'c'

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Snippet 4: Using __slots__ in Inheritance (Single Level)

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class Parent:
    __slots__ = ('x',)

class Child(Parent):
    __slots__ = ('y',)

obj = Child()
obj.x = 5
obj.y = 10
print(obj.x, obj.y)

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Snippet 5: Combining __slots__ with Class Variables

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class Config:
    __slots__ = ('host', 'port')
    version = "1.0"  # Class variable

c = Config()
c.host = "localhost"
c.port = 8080
print(Config.version, c.host, c.port)

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Snippet 6: Attempting to Use __dict__ with __slots__

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class Example:
    __slots__ = ('attr1', 'attr2')

obj = Example()
obj.attr1 = "Hello"
obj.attr2 = "World"
# print(obj.__dict__)  # AttributeError: 'Example' object has no attribute '__dict__'

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Snippet 7: Using __slots__ with Properties

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class Person:
    __slots__ = ('_name', '_age')

    def __init__(self, name, age):
        self._name = name
        self._age = age

    @property
    def name(self):
        return self._name

    @property
    def age(self):
        return self._age

p = Person("Alice", 30)
print(p.name, p.age)

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Snippet 8: Multiple Inheritance and __slots__

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class A:
    __slots__ = ('a',)

class B:
    __slots__ = ('b',)

class C(A, B):
    __slots__ = ('c',)

obj = C()
obj.a = 1
obj.b = 2
obj.c = 3
print(obj.a, obj.b, obj.c)

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Snippet 9: Performance Measurement with __slots__

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import timeit

class WithoutSlots:
    def __init__(self, x, y):
        self.x = x
        self.y = y

class WithSlots:
    __slots__ = ('x', 'y')

    def __init__(self, x, y):
        self.x = x
        self.y = y

def create_without_slots():
    obj = WithoutSlots(1, 2)

def create_with_slots():
    obj = WithSlots(1, 2)

print("Without __slots__:", timeit.timeit(create_without_slots, number=1000000))
print("With __slots__:", timeit.timeit(create_with_slots, number=1000000))

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Snippet 10: Extending __slots__ Dynamically (Workaround)

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class DynamicSlots:
    __slots__ = ('x', 'y')

    def __init__(self, x, y):
        self.x = x
        self.y = y

obj = DynamicSlots(1, 2)
setattr(obj, 'z', 3)  # Raises AttributeError

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