Not understand the difference and there uses

[fishhook]

== and != are operators of equality.
not is a logical operator that revers the value of a logical variable.

For understanding a difference just try to change "==" to "is_equal" and "!=" to "is_not_equal" functions.

def is_equal(a, b):
    return a == b

def not_is_equal(a, b):
    return a != b