Something about the sys.getrefcount

Question

After I ran "a.method",why the sys.getrefcount(a) returned 3? there was no new variable referred the object

class A(object):
   def method(): pass 

import sys
a=A()

sys.getrefcount(a) # returns 2

a.method
<bound method A.method of <__main__.A object at 0x7f1e73059b50>>

sys.getrefcount(a) # returns 3

Answer 1

In the python interactive shell, the result of the last command is stored in a special varialbe named _. Naturally, this variable holds a reference to that result.

In your case, the result is a method object, which holds a ref to its "self", i.e. the variable a. In other words, in the case you describe, the extra ref is indirect. The result (<bound method A.method of <__main__.A object at 0x7f1e73059b50>>) which is kept alive due to variable _, holds a reference to <__main__.A object at 0x7f1e73059b50>.