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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def get_hub():
 """Return the instance of the hub."""

    try:
        hub = _local.hub
    except AttributeError:
        # The Hub can only be instantiated from the root fiber. No other fibers
        # can run until the Hub is there, so the root will always be the first
        # one to call get_hub().
        assert fibers.current().parent is None
        hub = _local.hub = Hub()
    return hub