Cannot `create function` in plpython3u, permission denied
First don't make plpython3u into a trusted language.  This is bad.  You are giving access to all kinds of things on the database, the filesystem, and the like in ways that could be horribly abused.  Please reconsider.

Now from your comments you want to keep the admin permission separate from the normal user permission.  The way to do this is to make sure the superuser is NOINHERIT and the user is granted the role.  You can:

 CREATE ROLE mydba WITH SUPERUSER NOINHERIT;

 GRANT mydba TO myuser;


Then logged in as myuser then you can:

 SET ROLE mydba;


And you get superuser privileges.  You can use this to then to temporarily escalate your permissions in a way similar to sudo on *nix systems.