code: def set_stencil_op(self, sfail='keep', dpfail='keep', dppass='keep',
                         face='front_and_back'):
          
          self.glir.command('FUNC', 'glStencilOpSeparate', 
                            face, sfail, dpfail, dppass)
docs: Set front or back stencil test actions
      
          Parameters
          ----------
          sfail : str
              Action to take when the stencil fails. Must be one of
              'keep', 'zero', 'replace', 'incr', 'incr_wrap',
              'decr', 'decr_wrap', or 'invert'.
          dpfail : str
              Action to take when the stencil passes.
          dppass : str
              Action to take when both the stencil and depth tests pass,
              or when the stencil test passes and either there is no depth
              buffer or depth testing is not enabled.
          face : str
              Can be 'front', 'back', or 'front_and_back'.