class_docstr: Discrete Alpha Scale
  
  Parameters
  ----------
  {superclass_parameters}
code: def __init__(self, **kwargs):
      warn(
          "Using alpha for a discrete variable is not advised.",
          PlotnineWarning,
      )
      super().__init__(**kwargs)
  
imports: from warnings import warn
  import numpy
  from .._utils.registry import alias
  from ..doctools import document
  from ..exceptions import PlotnineWarning
  from .scale_continuous import scale_continuous
  from .scale_datetime import scale_datetime
  from .scale_discrete import scale_discrete
label_desc: Use image node_id 1 to create a new scale_alpha_discrete object from inherited base classes: scale_alpha_ordinal with example: obj = scale_alpha_discrete()