title: rotation of a point in 3D about an arbitrary axis using python
body: <p>If I have a point in 3D <code>(x,y,z)</code> and I need to rotate this point about an arbitrary axis that passes through two points <code>(x1,y1,z1)</code> and <code>(x2,y2,z2)</code> with an angle theta counterclockwise, how can I do this using python?</p>
  
  <p>I read a lot about 3D rotation, but I failed to make it using python, so please can anybody help?</p>