Question

I was quite surprised when

[] is not []

evaluated to True.

What is happening in this code? What really not and is statements are doing?

Answer 1

a is not b is a special operator which is equivalent to not a is b.

The operator a is b returns True if a and b are bound to the same object, otherwise False. When you create two empty lists you get two different objects, so is returns False (and therefore is not returns True).