How does addresses of -5 to 256 numbers work in Python?

Question

I'm just trying to get the addresses of variables in python and came across something odd.

I have assigned some numbers to a variable and checking the Equality and Identity of those variables.

>>>a=-10
>>>a is -10

Output:

False

---

>>>a=-5
>>>a is -5

Output:

True

---

>>>a=256
>>>a is 256

Output:

True

---

>>>a=257
>>>a is 257

Output:

False

I'm just curious what's happening behind the scenes in range -5 to 256.

Can someone please explain.

It's something like the one mentioned here - https://ubuntuforums.org/archive/index.php/t-1848655.html

I'm using:

Python: 3.7.5
Ubuntu: 18.04