How to compute frame transformations with Tf (ROS)

Here a script to compute the transformation between two frames published in /tf in ROS.
You can download the python script, modify the name of the topics and run it with
python computeTF2frames.py

The result:

Translation:  (0.06290424180516997, -0.004345408291908189, 1.1515618071559173)
Rotation:  (-0.5041371308002005, 0.5088056423602352, -0.49116582568647843, 0.4957002151791443)