def click_estimate_slope():
    """
    Takes two clicks and returns the slope.

    Right-click aborts.
    """

    c1 = _pylab.ginput()
    if len(c1)==0:
        return None

    c2 = _pylab.ginput()
    if len(c2)==0:
        return None

    return (c1[0][1]-c2[0][1])/(c1[0][0]-c2[0][0])
Takes two clicks and returns the slope.

    Right-click aborts.