Choosing at random an integer between 0 and the length of a given list, inclusive

In Python 3.x, I need to choose at random an integer between 0 and the length of a given list, inclusive. In other words, given

mylist = [0, 5, 6, 8, -10]

I want to return a number between 0 and 5, inclusive. What's the most Pythonic way to do it? I tried

import numpy as np
my_list = [0, 5, 6, 8, -10]
def choose_at_random(a_list):
    choice = np.random.randint(0, len(a_list) + 1)
    return choice   

This works, but is this the Pythonic way to do it? The need to +1 the list length seems a bit error-prone (I mean, it's easy to forget to do it).