<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def preferences(self, section=None):
 """ Return a list of all registered preferences or a list of preferences registered for a given section :param section: The section name under which the preference is registered :type section: str. :return: a list of :py:class:`prefs.BasePreference` instances """


        if section is None:
            return [self[section][name] for section in self for name in self[section]]
        else:
            return [self[section][name] for name in self[section]]