Why random.shuffle(list(range(n))) works, but random.shuffle(range(n)) does not?

Question

When, in Python 3, using random module random.shuffle(list(range(n))) works, but random.shuffle(range(n)) does not.

Why is it so?

When I type type(range(n)) it returns range.

Answer 1

Python 3's range now returns an range-object (beeing an immutable sequence) and not a list (like Python 2)!

A range-object (besides other differences) does not support item assignment, which is the error you observe (probably):

File ".../random.py", line 272, in shuffle
    x[i], x[j] = x[j], x[i]
TypeError: 'range' object does not support item assignment

The line 272 is the pythonic-way of swapping two variables in python, which is a common operation in most shuffle algorithms (like Fisher-Yates).

The docs also mentions this (if you want to shuffle sequences):

To shuffle an immutable sequence and return a new shuffled list, use sample(x, k=len(x)) instead

So this will work (and is equivalent given the task of shuffling):

shuffled_list = random.sample(range(n), k=n)

Your approach of creating a list first is also fine, if you can afford the memory/time needed to do that.