Python: error with random.sample() while creating a list of lists from another list

I have a list of positive integers like this:

mainlist=[0,1,2,3,...,3999]

And out of it I want to generate a list of 50 lists, where each sublist has increasing length (10, 20, 30,..., 500). Each sublist element is a random.sample() selection of values from mainlist.

This is my attempt (coming from here):

import random

mainlist=[i for i in range(4000)]
listoflists=[random.sample(mainlist, l) for l in range(10, 510, 10)]

However this gives me an error:

TypeError: random_sample() takes at most 1 positional argument (2 given)

Why is that so? I am using Python 2.7.11 32-bit with Jupyter on Windows 8.1