27. Python's Garbage Collection

This Python code snippets demonstrating concepts related to Python's garbage collection and memory management:

1. Manually Triggering Garbage Collection

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import gc

class Demo:
    def __del__(self):
        print("Object destroyed.")

obj = Demo()
del obj  # Object eligible for garbage collection
gc.collect()  # Manually trigger garbage collection

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2. Reference Counting

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import sys

class Demo:
    pass

obj = Demo()
print(sys.getrefcount(obj))  # Get reference count
ref = obj
print(sys.getrefcount(obj))  # Reference count increases with another reference
del ref
print(sys.getrefcount(obj))  # Reference count decreases after deletion

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3. Cyclic References

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import gc

class A:
    def __init__(self):
        self.ref = None

a = A()
b = A()
a.ref = b
b.ref = a  # Creates a reference cycle

del a
del b

# Objects won't be freed immediately due to the cycle, but garbage collector will handle it
gc.collect()

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4. Disabling Garbage Collection

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import gc

gc.disable()  # Disable garbage collection
print("Garbage collection disabled:", gc.isenabled())  # Check if disabled

gc.enable()  # Enable garbage collection
print("Garbage collection enabled:", gc.isenabled())

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5. Tracking Unreachable Objects

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import gc

class Demo:
    pass

a = Demo()
b = Demo()
a.ref = b
b.ref = a  # Cyclic reference

del a
del b

unreachable = gc.collect()  # Trigger garbage collection
print(f"Unreachable objects collected: {unreachable}")

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6. Weak References

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import weakref

class Demo:
    pass

obj = Demo()
weak_ref = weakref.ref(obj)  # Create a weak reference
print(weak_ref())  # Access the object via weak reference

del obj  # Delete the strong reference
print(weak_ref())  # None: object has been garbage collected

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7. Customizing Object Finalization with __del__

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class Demo:
    def __del__(self):
        print(f"Instance of {self.__class__.__name__} deleted.")

obj = Demo()
del obj  # __del__ is called when the object is destroyed

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8. Memory Management with Generations

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import gc

gc.set_debug(gc.DEBUG_LEAK)  # Enable debug mode
print("Garbage collection thresholds:", gc.get_threshold())  # Get thresholds for generations

# Set custom thresholds
gc.set_threshold(100, 10, 10)
print("Updated thresholds:", gc.get_threshold())

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9. Viewing Objects in Garbage

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import gc

class Demo:
    pass

a = Demo()
b = Demo()
a.ref = b
b.ref = a  # Cyclic reference

del a
del b

gc.collect()
print("Garbage objects:", gc.garbage)

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10. Memory Management with id and del

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class Demo:
    pass

obj = Demo()
print(f"Object ID before deletion: {id(obj)}")

del obj

try:
    print(f"Object ID after deletion: {id(obj)}")
except NameError:
    print("Object no longer exists.")

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These snippets illustrate Python's garbage collection mechanisms, including reference counting, cyclic garbage collection, weak references, and manual garbage collection controls. This understanding helps optimize memory usage and avoid common pitfalls like memory leaks.