@Appender(rwindow.expanding.__doc__)
def expanding(self, min_periods=1, center=False, axis=0):
    axis = self._get_axis_number(axis)
    return rwindow.expanding(self, min_periods=min_periods, center=center, axis=axis)
@Appender(rwindow.expanding.__doc__)
def expanding(self, min_periods=1, center=False, axis=0):
    axis = self._get_axis_number(axis)
    return rwindow.expanding(self, min_periods=min_periods, center=center, axis=axis)