def unregister(self, obj=None):
if obj is None:<EOL><INDENT>self.__databases.clear()<EOL>self.__schemas.clear()<EOL><DEDENT>elif isinstance(obj, orb.Schema):<EOL><INDENT>self.__schemas.pop(obj.name(), None)<EOL><DEDENT>elif isinstance(obj, orb.Database):<EOL><INDENT>if obj == self.__current_db:<EOL><INDENT>self.__current_db = None<EOL><DEDENT>self.__databases.pop(obj.name(), None)<EOL><DEDENT>else:<EOL><INDENT>self.__current_db = None<EOL>self.__schemas.pop(obj, None)<EOL>self.__databases.pop(obj, None)<EOL><DEDENT>
Unregisters the object from the system.  If None is supplied, then
all objects will be unregistered

:param obj: <str> or <orb.Database> or <orb.Schema> or None