python - 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.