'Parameters
norm : :class:`matplotlib.colors.Normalize` instance
The normalizing object which scales data, typically into the
interval ``[0, 1]``.
If *None*, *norm* defaults to a *colors.Normalize* object which
initializes its scaling based on the first data processed.
cmap : str or :class:`~matplotlib.colors.Colormap` instance
The colormap used to map normalized data values to RGBA colors.'

def __init__(self, norm=None, cmap=None):

    self.callbacksSM = cbook.CallbackRegistry()
    if (cmap is None):
        cmap = get_cmap()
    if (norm is None):
        norm = colors.Normalize()
    self._A = None
    self.norm = norm
    self.cmap = get_cmap(cmap)
    self.colorbar = None
    self.update_dict = {u'array': False}
