First - and important thing:

while p is not None and p.data is not value:

You comparison p.data is not value is something different from p.data != value - and I guest that you wanted the second.

is means the same object, while == means the same value (of optionally different objects). For small integers - as in your test - Python uses the same predefined object but for e. g. 500 or -50 it is not true - try in your interpreter

500 + 1 is 501

and you will obtain False.

Second, you need not compare to None (or to 0, or to '', etc.) as its boolean value is False. So the same command - in this case the correct one - may be

while not p and p.data != value:

First - and important thing:

while p is not None and p.data is not value:

You comparison p.data is not value is something different from p.data != value - and I guest that you wanted the second.

is means the same object, while == means the same value (of optionally different objects). For small integers - as in your test - Python uses the same predefined object but for e. g. 500 or -50 it is not true - try in your interpreter

500 + 1 is 501

and you will obtain False.

Second, you need not compare to None (or to 0, or to '', etc.) as its boolean value is False. So the same command - in this case the correct one - may be

while not p and p.data != value:

(and similarly for your other commands).