This is in the standard python 3.7.3 install under Debian 10.  It's possible that this is on purpose, and it's (separately) possible that the Debian packagers did this for some reason.  I'm not sure it's a bug but am reporting it as it's an oddity that might warrant looking into.

When I look at sys.path in the IDLE shell, the path includes /usr/bin, which is not there under the normal python prompt.  Since /usr/bin is not a place where python modules usually live, it's a bit strange to find it on the path.  It doesn't seem healthy since it could lead to surprises.  But maybe I'm missing something.

Feel free to close this if the inclusion is intentional.