Python "in" operator speed

Question

Is the in operator's speed in python proportional to the length of the iterable?

So,

len(x) #10
if(a in x): #lets say this takes time A
    pass

len(y) #10000
if(a in y): #lets say this takes time B
    pass

Is A > B?

Answer 1

There's no general answer to this: it depends on the types of a and especially of b. If, for example, b is a list, then yes, in takes worst-case time O(len(b)). But if, for example, b is a dict or a set, then in takes expected-case time O(1) (i.e., constant time).

About "Is A > B?", you didn't define A or B. As above, there's no general answer to which of your in statements will run faster.

Answer 2

A summary for in:

list - Average: O(n)
set/dict - Average: O(1), Worst: O(n)

See this for more details.