code: def _interpolate(self, factor, minGlyph, maxGlyph,
                       round=True, suppressError=True):
          
          minGlyph = minGlyph._toMathGlyph()
          maxGlyph = maxGlyph._toMathGlyph()
          try:
              result = interpolate(minGlyph, maxGlyph, factor)
          except IndexError:
              result = None
          if result is None and not suppressError:
              raise FontPartsError(("Glyphs '%s' and '%s' could not be "
                                    "interpolated.")
                                   % (minGlyph.name, maxGlyph.name))
          if result is not None:
              if round:
                  result = result.round()
              self._fromMathGlyph(result, toThisGlyph=True)
docs: Subclasses may override this method.