How to use random.shuffle() on a generator? python

It's not possible to randomize the yield of a generator without temporarily saving all the elements somewhere. Luckily, this is pretty easy in Python:

tmp = list(yielding(x))
random.shuffle(tmp)
for i in tmp:
    print i

Note the call to list() which will read all items and put them into a list.

If you don't want to or can't store all elements, you will need to change the generator to yield in a random order.

In order to shuffle the sequence uniformly, random.shuffle() needs to know how long the input is. A generator cannot provide this; you have to materialize it into a list:

lst = list(yielding(x))
random.shuffle(lst)
for i in lst:
    print i

You could, instead, use sorted() with random.random() as the key:

for i in sorted(yielding(x), key=lambda k: random.random()):
    print(i)

but since this also produces a list, there is little point in going this route.

Demo:

>>> import random
>>> x = [1,2,3,4,5,6,7,8,9]
>>> sorted(iter(x), key=lambda k: random.random())
[9, 7, 3, 2, 5, 4, 6, 1, 8]