Unexpected result from sys.getrefcount

Question

When I typed:

>>> astrd = 123
>>> import sys
>>> sys.getrefcount(astrd)
3
>>> 

I am not getting where is astrd used 3 times ?

Answer 1

It's not astrd that is referenced three times, but the value 123. astrd is simply a name for the (immutable) number 123, which can be referenced however many times. Additionally to that, small integers are usually shared:

>>> astrd = 123
>>> sys.getrefcount(astrd)
4
>>> j = 123
>>> sys.getrefcount(astrd)
5

In the second assignment, no new integer is created, instead j is just a new name for the integer 123.

However, given very large integers, this does not hold:

>>> i = 823423442583
>>> sys.getrefcount(i)
2
>>> j = 823423442583
>>> sys.getrefcount(i)
2

Shared integers are an implementation detail of CPython (among others). Since small integers are instantiated very often, sharing them saves a lot of memory. This is made possible by the fact that integers are immutable in the first place.

For the additional reference in the second example, cf. codeape's answer.

Answer 2

From the getrefcount docstring:

... The count returned is generally one higher than you might expect, because it includes the (temporary) reference as an argument to getrefcount().

The other two references means that python internally is holding two references to the object. Maybe the locals() and globals() dictionaries count as one reference each?