Why is mpl_toolkits loaded?

[Serafim]

I think that you just have a reference to it. It is not imported. Find out how with

python -v

(beware of massive output).
You will probably find a line like

# possible namespace for /<some path...>/site-packages/mpl_toolkits

Also see what happens with

python -S # Don't load the "site" module
>>> import sys
>>> sys.modules

It should not appear in the output. If it does I'll be very puzzled. Not loading the site module means, among other things, that the site-packages directories aren't added to the module path at initialization.