<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def kde_none(events_x, events_y, xout=None, yout=None):
 """ No Kernel Density Estimation Parameters events_x, events_y: 1D ndarray The input points for kernel density estimation. Input is flattened automatically. xout, yout: ndarray The coordinates at which the KDE should be computed. If set to none, input coordinates are used. Returns ------- density: ndarray, same shape as `xout` The KDE for the points in (xout, yout) Notes ----- This method is a convenience method that always returns ones in the shape that the other methods in this module produce. """

    valid_combi = ((xout is None and yout is None) or
                   (xout is not None and yout is not None)
                   )
    if not valid_combi:
        raise ValueError("Both `xout` and `yout` must be (un)set.")

    if yout is None and yout is None:
        xout = events_x
        yout = events_y

    return np.ones(xout.shape)