def METHOD_NAME(iterator: Iterable[Iterable[T]]) -> Iterator[T]:
  """Flattens nested iterables into one iterator.
  Examples:
    >>> list(Flatten([[1, 2, 3], [4, 5, 6]]))
    [1, 2, 3, 4, 5, 6]
    >>> list([range(3), range(5), range(3)])
    [0, 1, 2, 0, 1, 2, 3, 4, 0, 1, 2]
  Args:
    iterator: An iterator of iterators to flatten.
  Yields:
    Items yielded by the given iterators.
  """
  for items in iterator:
    for item in items:
      yield item