import numpy as np

class Trajectory(object):
    def __init__(self,v0=(1,2,3)):

        self.vec = v0
        self.x   = v0[0]
        self.y   = v0[1]
        self.z   = v0[2]

   def vector_transformation(self):
        #self.vec = some complicated manipulation of v0
        self.x   = self.vec[0]
        self.y   = self.vec[1]
        self.z   = self.vec[2]