class-2-find-the-torsional-angle.py

class Points(object):
    def __init__(self, x, y, z):
        self.x, self.y, self.z = x, y, z

    def __sub__(self, no):
        return Points(self.x - no.x,
                      self.y - no.y,
                      self.z - no.z)

    def dot(self, no):
        return self.x*no.x + self.y*no.y + self.z*no.z

    def cross(self, no):
        return Points(self.y*no.z - self.z*no.y,
                      self.z*no.x - self.x*no.z,
                      self.y*no.x - self.x*no.y)
        
    def absolute(self):
        return pow((self.x ** 2 + self.y ** 2 + self.z ** 2), 0.5)