def __init__(self, sdat):
self.sdat = sdat<EOL>self._last = UNDETERMINED<EOL>self._data = {None: _step.EmptyStep()}<EOL>
Initialization of instances:

        Args:
            sdat (:class:`StagyyData`): the StagyyData instance owning the
                :class:`_Steps` instance.
        Attributes:
            sdat (:class:`StagyyData`): the StagyyData instance owning the
                :class:`_Steps` instance.