Writing a little Python-script for calculating time dilation

Yes, I know, I can do that in Google Sheets on a single cell.
But you never know if it is around in the future when you need it :P

So just for fun I'm writing a simple Python script to calculate the time dilation and remind me everywhere that you don't need to travel faster than light (which is impossible) or even with the speed of light to reach destinations thousands of light years away theoretically.