To use mumax3 as a calculator instead of OOMMF use the following import at the top of your notebook

import mumax3c as mc

and replace oc with mc in the examples.

Note, that mumax3c (the interface to mumax3) does not support everything supported by oommfc (and OOMMF). Refer to Compatibility: Ubermag - OOMMF - mumax3 for details.