ArcPy Label Class object returning unexpected value for expression property?

Question

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd, "TestFile_LineToPoints13_Prod"):
    if lyr.supports("LABELCLASSES"):
        for lblclass in lyr.labelClasses:            
            lblclass.expression = " [OBJECTID]"
            if lblClass.showClassLabels:
                    print "    Class Name:  " + lblClass.className
                    print "    Expression:  " + lblClass.expression
mxd.save()
del mxd

Prints:

Class Name: Default

Expression: [Shape_Length]

The label for that layer is even set at ObjectID and is currently showing the labels... Why does it keep responding Shape_Length?

Answer 1

Try this code instead which I think will work because I tested it.

I suspect:

lblclass.expression = " [OBJECTID]"

should be:

lblclass.expression = "[OBJECTID]"

I also changed lblclass to lblClass in two places and used some more print statements while I was debugging.

import arcpy
mxd = arcpy.mapping.MapDocument("CURRENT")
for lyr in arcpy.mapping.ListLayers(mxd, "TestFile_LineToPoints13_Prod"):
    print lyr.name
    if lyr.supports("LABELCLASSES"):
        print lyr.name + " supports label classes"
        for lblClass in lyr.labelClasses:
            print lblClass.className
            lblClass.expression = "[OBJECTID]"
            if lblClass.showClassLabels:
                    print "    Class Name:  " + lblClass.className
                    print "    Expression:  " + lblClass.expression
mxd.save()
del mxd