How to rename unique value using arcpy

Question

I work with several MXD files. In each map there a polygon layer with unique values:

I try to change in the table of contents the "a" into "land use" by using this code:

import arcpy,os,sys
from arcpy import env

env.workspace = r"G:\desktop\Project"
for mxdname in arcpy.ListFiles("*.mxd"):
    print mxdname 
    mxd = arcpy.mapping.MapDocument(r"G:\desktop\Project\\" + mxdname)
    df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0] 
    lyr = arcpy.mapping.ListLayers(mxd, "*")[0]
    if lyr.symbologyType == "UNIQUE_VALUES":
        vals = lyr.symbology.classLabels
        for v in vals:
            if v == "a":
                print lyr.name
                v = 'landUse'
                print v   
    mxd.save()
del mxd 

I just want to change the name in the table of content, and not change the attribute table value. When running this code i get this result and with no change in the maps:

>>> 
project.mxd
polygon
landUse
>>>    

Answer 1

To update the labels, you'll need to update them all at once by providing a list to lyr.symbology.classLabels.

if lyr.symbologyType == "UNIQUE_VALUES":
    vals = lyr.symbology.classLabels
    newLabels = []
    for v in vals:
        if v == "a":
            v = 'landUse'
        newLabels.append(v)  # push each label into the list
    lyr.symbology.classLabels = newLabels  # apply the new labels
mxd.save()