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import random
def _uniform_rng():
while True:
yield random.uniform(0, 1)
_rng = _uniform_rng()
def poprandom(sequence, rng=_rng):
index = int(round(next(rng) * (len(sequence) - 1)))
item = sequence[index]
# It's O(1) to pop the last item, and O(n) to pop any other item. So we'll
# always pop the last item and put it in the slot vacated by the item we're
# popping.
last_item = sequence.pop()
if index < len(sequence):
sequence[index] = last_item
return item
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