code: def set_alpha(self, alpha):
      super().set_alpha(alpha)
      _alpha = self.get_alpha()
      rgb = self._rgb
      if self.get_forced_alpha():
          self.ctx.set_source_rgba(rgb[0], rgb[1], rgb[2], _alpha)
      else:
          self.ctx.set_source_rgba(rgb[0], rgb[1], rgb[2], rgb[3])
  
imports: import functools
  import gzip
  import math
  import numpy
  from ..None import _api, cbook, font_manager
  from matplotlib.backend_bases import _Backend, FigureCanvasBase, FigureManagerBase, GraphicsContextBase, RendererBase
  from matplotlib.font_manager import ttfFontProperty
  from matplotlib.path import Path
  from matplotlib.transforms import Affine2D
label_desc: Use image node_id 3 for calling the GraphicsContextCairo obj's underlying member method code with example usage: obj.set_alpha(alpha) without return types