How is the Garbage Collector organized in Python? How are cyclic references detected?

In Python, the garbage collector (GC) is based on reference counting and is supplemented with a cycle detection mechanism.

• Reference counting — each object has a reference count. When the count reaches 0, the object is immediately deleted.
• Cycle problem — if objects reference each other but are not accessible from the program, their counts do not reach 0, and they are not deleted.

To solve this problem, Python uses the gc module, which periodically runs a cycle detection algorithm:

• GC tracks objects involved in cycles (usually objects with __del__ methods or containers).
• It builds a graph of objects and searches for cycles that are unreachable from root objects.
• Detected cycles are removed, freeing memory.

Example usage:

import gc

# Enable the cycle collector
gc.enable()

# Run collection manually
gc.collect()

Thus, Python combines fast reference counting with periodic cycle detection for efficient memory management.