is vs ==
Difference
is checks if two variables are pointing to the same object in memory.== checks if the object pointed by each of the variable are equal via __eq__().
Example
>>> a = [1, 2, 3]
>>> b = a
>>> b is a
True
>>> b == a
True
# Make a new copy of list `a` via the slice operator,
# and assign it to variable `b`
>>> b = a[:]
>>> b is a
False
>>> b == a
True
# `is` accidently works as CPython caches small integer objects.
# However, a SyntaxWarning will be produced in Python 3.8+.
>>> 1000 is 10**3
<stdin>:1: SyntaxWarning: "is" with 'int' literal. Did you mean "=="?
True
>>> 1000 == 10**3
True
References