code: def expand_default(self, scale, discrete=(0, 0.6, 0, 0.6),
                         continuous=(0.05, 0, 0.05, 0)):
          
          if is_waive(scale.expand):
              if isinstance(scale, scale_discrete):
                  return discrete
              elif isinstance(scale, scale_continuous):
                  return continuous
              else:
                  name = scale.__class__.__name__
                  msg = "Failed to expand scale '{}'".format(name)
                  raise PlotnineError(msg)
          else:
              return scale.expand
docs: Expand a single scale