Why is a reference counter used in Python?

The reference count in Python is used for automatic memory management, implemented through a garbage collector. It tracks the number of references to an object in memory.

When the reference count for an object reaches zero, it means that no variables or data structures refer to this object anymore. In this case, the garbage collector determines that the memory occupied by the object can be freed and returned to the operating system for reuse.

This helps prevent memory leaks, where memory occupied by objects remains inaccessible, and at the same time relieves the developer from manually managing memory allocation and deallocation, as in languages with manual memory management (e.g., C/C++).

# Creating an object. Its reference count is 1.
a = [1, 2, 3]

# Another reference to the same object. The reference count increases.
b = a

# A function that shows the reference count (used by Python's internal structure)
import sys
print(sys.getrefcount(a)) # Will output approximately 3 (including the reference from sys.getrefcount)

# Deleting one reference. The count decreases.
del b
print(sys.getrefcount(a)) # The count will decrease

# Deleting the last reference. The count becomes 0.
del a
# Now the object [1, 2, 3] can be collected by the garbage collector.

However, reference counting alone cannot handle cyclic references (when objects refer to each other, but there are no external references to the entire group of objects). To solve this problem, Python uses an additional cyclic garbage collector that periodically searches for and removes such cycles.

As a result, reference counting is the main memory management mechanism in CPython (the main implementation of Python), allowing efficient and automatic management of object lifecycles in memory.