Python reference count manipulation

pyrefs.py

# coding: utf-8


import sys
import gc
import ctypes


# configuration of Py_IncRef and Py_DecRef
_c_inc_ref = ctypes.pythonapi.Py_IncRef
_c_inc_ref.argtypes = [ctypes.py_object]
_c_dec_ref = ctypes.pythonapi.Py_DecRef
_c_dec_ref.argtypes = [ctypes.py_object]


def inc_ref(obj, n=1):
    """
    Increases the reference count of an object *obj* by *n*.
    """
    for _ in range(n):
        _c_inc_ref(obj)


def dec_ref(obj, n=1, collect=True):
    """
    Decreases the reference count of an object *obj* by *n*. When *collect* is *True*, the garbage
    collector is initiated afterwards.
    """
    for _ in range(n):
        _c_dec_ref(obj)

    if collect:
        gc.collect()


def ref_count(obj):
    """
    Returns the number of references to an object *obj*.
    """
    # subtract 3 for: function argument, reference in getrefcount, and the function stack
    return sys.getrefcount(obj) - 3
    # return len(gc.get_referrers(obj)) - 1


if __name__ == "__main__":
    # some tests which print (expected value, actual value)

    obj = object()
    print(1, ref_count(obj))
    obj2 = obj
    print(2, ref_count(obj))
    del obj2
    print(1, ref_count(obj))
    inc_ref(obj)
    print(2, ref_count(obj))
    dec_ref(obj)
    print(1, ref_count(obj))
    dec_ref(obj)
    print("random number", ref_count(obj))  # obj is garbage collected