<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _get_default(cls, attribute):
 """Return the default value for `attribute`. If no default is specified in this style, get the default from the nearest superclass. If `attribute` is not supported, raise a :class:`KeyError`."""

        try:
            for klass in cls.__mro__:
                if attribute in klass._attributes:
                    return klass._attributes[attribute].default_value
        except AttributeError:
            raise KeyError("No attribute '{}' in {}".format(attribute, cls))