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

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

Solution 1:

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.

Solution 2:

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.

Solution 3:

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”.

Solution 4:

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.