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How can I change the symbology of a layer with single symbol to unique values with Python. I don't know how to update it.

I used this code:

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
lyr = arcpy.mapping.ListLayers(mxd,"region")[0]
if lyr.symbologyType == "UNIQUE_SYMBOLE":
  lyr.symbology.valueField = "REGION"
  lyr.symbology.addAllValues()
arcpy.RefreshActiveView()
arcpy.RefreshTOC()
del mxd

The code runs but doesn't change anything (no error message) the problem is that I want to change the symbology of the layer displaid with single symbol to category "uniques values"?

  • Can you edit your Question to include your ArcGIS version and what happens (error message etc) when you run your code, please? – PolyGeo Dec 10 '13 at 22:17
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    lyr.symbologyType will never equal "UNIQUE_SYMBOLE". The list of possible values is: GRADUATED_COLORS, GRADUATED_SYMBOLS, OTHER, UNIQUE_VALUES and RASTER_CLASSIFIED as per the website on the layer class. – Fezter Dec 10 '13 at 22:56
  • @Fezter I think you should turn your comment into an answer – PolyGeo Aug 6 '16 at 4:31
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As commented by @Fezter:

lyr.symbologyType will never equal "UNIQUE_SYMBOLE". The list of possible values is: GRADUATED_COLORS, GRADUATED_SYMBOLS, OTHER, UNIQUE_VALUES and RASTER_CLASSIFIED as per the website on the layer class.

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  1. First manually create a layer file with a unique value symbology based on your single symbol layer (not shown below).
  2. Then use arcpy.mapping.UpdateLayer to update your single symbol layer

    mxd = arcpy.mapping.MapDocument("Current")
    df = arcpy.mapping.ListDataFrames(mxd)[0]
    
    updateLayer = arcpy.mapping.ListLayers(mxd, "single_symbol_layer", df)[0]
    sourceLayer = arcpy.mapping.Layer("unique_value_symbol_layer")
    arcpy.mapping.UpdateLayer(df,updateLayer,sourceLayer, symbology_only = True)
    
    if updateLayer.symbologyType == "UNIQUE_VALUES":
        updateLayer.symbology.valueField = "UniqueValueField"
        updateLayer.symbology.addAllValues()
    
    arcpy.RefreshActiveView()
    arcpy.RefreshTOC()
    

To ensure the values are ordered replace:

updateLayer.symbology.valueField = "UniqueValueField"
updateLayer.symbology.addAllValues()

with

updateLayer.symbology.classValues = listofUniqueValues
updateLayer.symbology.showOtherValues = False

You can create the listofUniqueValues by:

listofUniqueValues = sorted({row[0] for row in arcpy.da.SearchCursor("single_symbol_layer", ["UniqueValueField"]) if row[0]})

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