How does the automatic memory management mechanism recognize and delete objects that reference each other cyclically?

Python's automatic memory management mechanism is based on reference counting and a garbage collector for cyclic references.

Reference counting tracks how many objects refer to a given object. When the count reaches zero, the object is deleted.

However, with cyclic references, objects refer to each other, and the counts do not reach zero, even if they are inaccessible from outside. To solve this problem, Python uses a garbage collector that periodically searches for object cycles that are unreachable from the program and deletes them.

The garbage collector is implemented in the gc module. It analyzes the object graph, detects cycles, and frees memory, preventing leaks.

Example:

import gc

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

a = A()
b = A()
a.ref = b
b.ref = a  # cyclic reference

# Remove external references
del a
del b

# Objects remain in memory due to the cycle, but the garbage collector will clean them up
gc.collect()  # force garbage collection