def interpolatePoint(pt1, pt2, v):
    """
    interpolate point by factor v

    >>> interpolatePoint((0, 0), (10, 10), 0.5)
    (5.0, 5.0)
    >>> interpolatePoint((0, 0), (10, 10), 0.6)
    (6.0, 6.0)
    """
    (xa, ya), (xb, yb) = pt1, pt2
    if not isinstance(v, tuple):
        xv = v
        yv = v
    else:
        xv, yv = v
    return xa + (xb - xa) * xv, ya + (yb - ya) * yv
