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Is there a way to get the current ref count of an object in Python?

GEOCHET
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5 Answers5

146

According to the Python documentation, the sys module contains a function:

import sys
sys.getrefcount(object) #-- Returns the reference count of the object.

Generally 1 higher than you might expect, because of object arg temp reference.

Taku
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tehvan
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    Link to the official documentation: https://docs.python.org/2/library/sys.html#sys.getrefcount – moi Aug 22 '16 at 13:41
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    To explain the "1 higher" comment, calling a function creates a temporary reference to the variable used as the parameter. – Mark Ransom Jan 29 '23 at 19:44
79

Using the gc module, the interface to the garbage collector guts, you can call gc.get_referrers(foo) to get a list of everything referring to foo.

Hence, len(gc.get_referrers(foo)) will give you the length of that list: the number of referrers, which is what you're after.

See also the gc module documentation.

T.C.
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kquinn
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    It should also be mentioned the count will be +1, since the gc list refers to the object, too. – Richard Levasseur Feb 04 '09 at 07:38
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    I think @Dan that the answer is correct: >>> import gc >>> class Bar(): ... pass ... >>> b = Bar() >>> len(gc.get_referrers(b)) 1 >>> gc.get_referrers(b) [{'b': <__main__.Bar instance at 0x7f1f010d0e18>, 'Bar': , '__builtins__': , '__package__': None, 'gc': , '__name__': '__main__', '__doc__': None}] – Havok Jan 11 '16 at 22:34
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    @tehvan's answer (`sys.getrefcount(object)`) is more straightforward than `len(gc.get_referrers(foo))`, if you really only need the number. – moi Aug 22 '16 at 13:43
  • in Android's qpython3, it gives wrong answer. every time. – Shihab Shahriar Khan Feb 18 '17 at 20:21
12

There is gc.get_referrers() and sys.getrefcount(). But, It is kind of hard to see how sys.getrefcount(X) could serve the purpose of traditional reference counting. Consider:

import sys

def function(X):
    sub_function(X)

def sub_function(X):
    sub_sub_function(X)

def sub_sub_function(X):
    print sys.getrefcount(X)

Then function(SomeObject) delivers '7',
sub_function(SomeObject) delivers '5',
sub_sub_function(SomeObject) delivers '3', and
sys.getrefcount(SomeObject) delivers '2'.

In other words: If you use sys.getrefcount() you must be aware of the function call depth. For gc.get_referrers() one might have to filter the list of referrers.

I would propose to do manual reference counting for purposes such as “isolation on change”, i.e. “clone if referenced elsewhere”.

Taku
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Frank-Rene Schäfer
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9
import ctypes

my_var = 'hello python'
my_var_address = id(my_var)

ctypes.c_long.from_address(my_var_address).value

ctypes takes address of the variable as an argument. The advantage of using ctypes over sys.getRefCount is that you need not subtract 1 from the result.

dejanualex
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Gautam Vanama
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    While funny this method should not be used: 1) nobody will understand what is going on while reading the code 2) it depends on implementation details of CPython: id being the address of the object and the exact memory layout of a PyObject. Just substract 1 from getrefcount() if needed. – ead Sep 06 '20 at 09:48
2

Every object in Python has a reference count and a pointer to a type. We can get the current reference count of an object with the sys module. You can use sys.getrefcount(object), but keep in mind that passing in the object to getrefcount() increases the reference count by 1.

import sys

name = "Steve"

# 2 references, 1 from the name variable and 1 from getrefcount
sys.getrefcount(name)
Utkarsh
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