code: def duplicateLayer(self, layerName, newLayerName):
          
          layerOrder = self.layerOrder
          layerName = normalizers.normalizeLayerName(layerName)
          if layerName not in layerOrder:
              raise ValueError("No layer with the name '%s' exists." % layerName)
          newLayerName = normalizers.normalizeLayerName(newLayerName)
          if newLayerName in layerOrder:
              raise ValueError("A layer with the name '%s' already exists." % newLayerName)
          newLayer = self._duplicateLayer(layerName, newLayerName)
          newLayer = normalizers.normalizeLayer(newLayer)
          return newLayer
docs: Duplicate the layer with **layerName**, assign
          **newLayerName** to the new layer and insert the
          new layer into the font. ::
  
              >>> layer = font.duplicateLayer("layer 1", "layer 2")