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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 wnfetd(window, n):
 """ Fetch a particular interval from a double precision window. http://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/wnfetd_c.html :param window: Input window :type window: spiceypy.utils.support_types.SpiceCell :param n: Index of interval to be fetched. :type n: int :return: Left, right endpoints of the nth interval. :rtype: tuple """

    assert isinstance(window, stypes.SpiceCell)
    assert window.dtype == 1
    n = ctypes.c_int(n)
    left = ctypes.c_double()
    right = ctypes.c_double()
    libspice.wnfetd_c(ctypes.byref(window), n, ctypes.byref(left),
                      ctypes.byref(right))
    return left.value, right.value