get a tangent vector from an edge in FreeCAD

tangent.py

def getTangent(edge):
    "Returns a tangent vector from an edge in FreeCAD"
    if isinstance(edge.Curve,Part.Line):
        vec = edge.Vertexes[-1].Point.sub(edge.Vertexes[0].Point)
    elif isinstance(edge.Curve,Part.Circle):
        v1 = edge.Vertexes[-1].sub(edge.Curve.Center)
        v2 = edge.Curve.Axis
        vec = v1.cross(v2)
    else:
        print "not supported"
        vec = None
    return vec