How to Use __slots__ in Python

# Regular class
class RegularPoint:
    def __init__(self, x, y):
        self.x = x
        self.y = y

# Class with __slots__
class OptimizedPoint:
    __slots__ = ['x', 'y']
    
    def __init__(self, x, y):
        self.x = x
        self.y = y

# Create instances
regular = RegularPoint(1, 2)
optimized = OptimizedPoint(1, 2)

# Memory comparison
import sys
print(f"Regular point size: {sys.getsizeof(regular)} bytes")
print(f"Regular point dict: {sys.getsizeof(regular.__dict__)} bytes")
print(f"Optimized point size: {sys.getsizeof(optimized)} bytes")

# Regular class allows dynamic attributes
regular.z = 3
print(f"\nRegular with z: {regular.z}")

# Optimized class does not
try:
    optimized.z = 3
except AttributeError as e:
    print(f"\nOptimized error: {e}")

# Multiple instances comparison
regulars = [RegularPoint(i, i) for i in range(1000)]
optimizeds = [OptimizedPoint(i, i) for i in range(1000)]

regular_total = sum(sys.getsizeof(p) + sys.getsizeof(p.__dict__) for p in regulars)
optimized_total = sum(sys.getsizeof(p) for p in optimizeds)

print(f"\n1000 regular points: {regular_total:,} bytes")
print(f"1000 optimized points: {optimized_total:,} bytes")
print(f"Savings: {regular_total - optimized_total:,} bytes")

# __slots__ with inheritance
class Base:
    __slots__ = ['x']

class Derived(Base):
    __slots__ = ['y']
    
    def __init__(self, x, y):
        self.x = x
        self.y = y

point = Derived(1, 2)
print(f"\nDerived point: x={point.x}, y={point.y}")