is and '=='

From blog.lerner.co.il/why-you-should-almost-never-use-is-in-python

a="beta"
b=a

id(a)
3072868832L

id(b)
3072868832L

Is the content of a and b the same? Yes.

a==b
True

Are a and b pointing to the same object?

a is b
True

id(a)==id(b)
True

So it's safer to use '==', but for example for comparing to None, it's more readable and faster when writing :

if x is None:
    print("x is None!")

This works because the None object is a singleton.