Get list of layer’s symbology classes and symbol labels using ArcPy?

Bud

I'm working with a FGDB FC that has data, of sorts, stored in the symbology. 
What I mean is: there is UNIT information in the symbology as labels, yet that UNIT information doesn't exist in a field in the attribute table of the FC anywhere.

Using ArcPy, is there a way to print a list of the layer’s symbology class values and symbol labels? I have 20+ layers, all with different symbology, so it would be ideal if I could do it programmatically.

If I could get a list, then I could manually:

• Copy/paste that list into a lookup table, either in Excel or right in the attribute table.
• Join from the layer to the lookup table via the common COLOR field.
• Use the field calculator to update a new UNIT field in the layer.
• Use the layer’s new UNIT field for analysis as required.

I’m new to ArcPy. I’ve tried to modify a couple of sample scripts online. But I don’t really know what I’m doing yet. Any tips would be appreciated.

ArcGIS Pro 3.0.3.

 

Related: Export symbology classes to a table

JohannesLindner

You can get the symbology of a layer. Form there, you'll have to follow the rabbit hole to the single symbology items.

This script will loop through a list of layers in the active map, analyze their symbology and add a new field to each layer with the symbology's label value:

layer_names = ["TestPolygons"]
aprx = arcpy.mp.ArcGISProject("current")

for name in layer_names:
    # get the layer
    layer = aprx.activeMap.listLayers(name)[0]
    # get the symbology fields and items
    renderer = layer.symbology.renderer
    fields = renderer.fields
    items = renderer.groups[0].items
    # create a dict {values: label}
    item_dict = {tuple(i.values[0]): i.label for i in items}
    # add a new field
    arcpy.management.AddField(layer, "Unit", "TEXT")
    # insert the label values
    with arcpy.da.UpdateCursor(layer, ["Unit"] + fields) as cursor:
        for row in cursor:
            key = tuple([str(x) for x in row[1:]])  # item.values stores values as string
            try:
                row[0] = item_dict[key]
                cursor.updateRow(row)
            except KeyError:  # no symbology found
                pass