code: def alpha(self, a):
      self._alpha = a
      self.fshader["alpha"] = float(a)
  
imports: from .base_filter import Filter
  from ..shaders import Function, Varying
  from ...color import colormap, Color
label_desc: Use image node_id 3 for calling the Alpha obj's underlying member method code with example usage: obj.alpha(a) without return types