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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 iterator_from_slice(s):
 """ Constructs an iterator given a slice object s. .. note:: The function returns an infinite iterator if s.stop is None """

    import numpy as np
    start = s.start if s.start is not None else 0
    step = s.step if s.step is not None else 1

    if s.stop is None:
        # Infinite iterator.
        return itertools.count(start=start, step=step)
    else:
        # xrange-like iterator that supports float.
        return iter(np.arange(start, s.stop, step))