To find vector between curve points.

vect.py

def vect(curv, pt2 = 1, pt1 = 0):
    """Returns a vector from two cvs on a curve. The argument curv is a PyMEL instance or string. For example:\vect('curve1', pt2 = 5, pt1 = 2) gives you a direction (i.e. vector) from cv[2] to cv[5] in curve1"""

    if type(curv) == str:
        curv = pm.ls(curv)[0]

    if curv.getShape().numCVs() <= pt2:
        print('\n!! There are {0} cvs. Make sure your pt2 value is less than {0}.  !!'.format(curv.getShape().numCVs()))
    else:
       return [curv.cv[pt2].getPosition()[0] - curv.cv[pt1].getPosition()[0],
               curv.cv[pt2].getPosition()[1] - curv.cv[pt1].getPosition()[1],
               curv.cv[pt2].getPosition()[2] - curv.cv[pt1].getPosition()[2]]