Applying symbology to raster layer in ArcPy without using symbology layer (layer file)?

Question

I have a raster layer with 3 unique values (1,2,3) and I want to apply a unique color to each using RGB values or hex codes, without the use of a symbology layer (layer file).

Is it possible to create a color map or symbology layer (layer file) entirely in ArcPy?

I want my code to add the raster layer to the map with the symbology I want (as opposed to random), but I don't want to use a pre-created symbology layer (layer file) or colormap - I would like the colors to be selected entirely in ArcPy, if possible.

arcpy.MakeRasterLayer_management(cat, "cat")
arcpy.SaveToLayerFile_management("cat", "cat.lyr", "ABSOLUTE") 
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
arcpy.mapping.AddLayer(df, "cat.lyr", "TOP")
# this is where I want to apply unique colors to each pixel value (pixel values are: 1,2,3)
# but I don't want to use add colormap or apply symbology from layer, unless the symbology
# layer or colormap can be created entirely in arcpy. I would like the color decisions
# to be made entirely in arcpy, without having to make a symbology layer or colormap 
# in the GUI
arcpy.RefreshActiveView()
arcpy.RefreshTOC()
del mxd, df

something like this?

colormap = open("colormap.clr", "w")
colormap.write("1 70 137 102\n")
colormap.write("2 255 176 59\n")
colormap.close()

Answer 1

You can do it like this:

# I'm assuming cat is the full path to a raster
# or a raster object

TempDir = os.environ.get("TEMP") # Your temp folder
ColFile = os.path.join(TempDir,"TEMP_CLR_FILE.clr")

with open(ColFile,'w') as ColWrite:
    ColWrite.write("1 255 0 0\n") # 1 = red
    ColWrite.write("2 0 0 255\n") # 2 = blue

arcpy.AddColormap_management(cat,input_CLR_file = ColFile)

arcpy.MakeRasterLayer_management(cat, "cat")
arcpy.SaveToLayerFile_management("cat", "cat.lyr", "ABSOLUTE") 
mxd = arcpy.mapping.MapDocument("CURRENT")
df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
arcpy.mapping.AddLayer(df, "cat.lyr", "TOP")
arcpy.RefreshActiveView()
arcpy.RefreshTOC()
del mxd, df
os.remove(ColFile) # clean up your mess

Write the colorfile on the fly with python file writing.. it's only a text file. Then remove the temp file after it has been applied; the file is not linked to the raster.

AddColormap has some specific requirements that need to be addressed.. please read the docs carefully as there's a few traps that will prevent this method from working.