'Set the alpha tranparencies of the collection.  *alpha* must be
a float or *None*.
ACCEPTS: float or None'

def set_alpha(self, alpha):

    if (alpha is not None):
        try:
            float(alpha)
        except TypeError:
            raise TypeError(u'alpha    must    be    a    float    or    None')
    artist.Artist.set_alpha(self, alpha)
    try:
        self._facecolors = mcolors.to_rgba_array(self._facecolors3d, self._alpha)
    except (AttributeError, TypeError, IndexError):
        pass
    try:
        self._edgecolors = mcolors.to_rgba_array(self._edgecolors3d, self._alpha)
    except (AttributeError, TypeError, IndexError):
        pass
    self.stale = True
