Copy button copies line numbers #251

>>> 1class Rock:
...  2    def __await__(self):
...  3        value_sent_in = yield 7
...  4        print(f"Rock.__await__ resuming with value: {value_sent_in}.")
...  5        return value_sent_in
...  6
...  7async def main():
...  8    print("Beginning coroutine main().")
...  9    rock = Rock()
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