code: def _interpolate(self, factor, minLayer, maxLayer, round=True,
                       suppressError=True):
          
          for glyphName in self.keys():
              del self[glyphName]
          for glyphName in minLayer.keys():
              if glyphName not in maxLayer:
                  continue
              minGlyph = minLayer[glyphName]
              maxGlyph = maxLayer[glyphName]
              dstGlyph = self.newGlyph(glyphName)
              dstGlyph.interpolate(factor, minGlyph, maxGlyph,
                                   round=round, suppressError=suppressError)
docs: This is the environment implementation of
          :meth:`BaseLayer.interpolate`.
  
          Subclasses may override this method.