Randomly shuffles an iterator

shuffle_iterator.py

import random

def shuffle(iterator, buffer_size):
    """ Uses a buffer to randomly shuffle items from an iterator  """
    
    # Fill the buffer
    buffer = []; cnt = 0
    item = next(iterator, None)
    while not item is None and cnt < buffer_size:
        buffer.append(item)
        item = next(iterator, None)
        cnt += 1

    random.shuffle(buffer)
    print('beginning iteration')
    while not item is None:
        # Randomly select from the buffer
        index = random.randint(0, cnt-1)
        yield buffer[index]
        # Replace the selected item
        buffer[index] = item
        item = next(iterator, None)
    
    # Empty the buffer
    while buffer:
        yield buffer.pop()