I've read Stack Overflow postings where, if you wait for one and a half minutes the port will free up and the server can then be started. This does not seem to happen in my case.
The only way to restart the server, other than a reboot, is to do the following:
$ ps -fA | grep python
The result will then give a line something like this:
root 2130 1 0 11:08 ? 00:00:00 sudo python bottlewebserver4.py
Then simply issue:
After this the bottlewebserver will start.
$ sudo kill 2130