Reference Counting

Each object counts how many references point to it and is freed when the count reaches zero.

Intermediate

import sys
a = []
sys.getrefcount(a)   # at least 2 (a + the function argument)
b = a                # count +1
del a                # count -1; object still alive through b

Deterministic freeing is why files are often closed promptly in CPython — but use with instead of relying on it.

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