warning about is

Starting Python 3.8, the interpreter warns about is comparison of literals.

Python 3.7:

>>> 0 is 0
True

Python 3.8:

>>> 0 is 0
<stdin>:1: SyntaxWarning: "is" with a literal. Did you mean "=="?
True

The reason is that it is an infamous Python gotcha. While == does values comparison (which is implemented by calling __eq__ magic method, in a nutshell), is compares memory addresses of objects. It's true for ints from -5 to 256 but it won't work for ints out of this range or for objects of other types:

a = -5
a is -5   # True
a = -6
a is -6   # False
a = 256
a is 256  # True
a = 257
a is 257  # False