Why is “1000000000000000 in range(1000000000000001)” so fast in Python 3?

Question

It is my understanding that the range() function, which is actually an object type in Python 3, generates its contents on the fly, similar to a generator.

Answer 1

Try x-1 in (i for i in range(x)) for large x values, which uses a generator comprehension to avoid invoking the range.__contains__ optimisation.