How to insert layer excluding MXD files using arcpy?

Question

I'm working on 24 MXD files. Several maps include "roads" layer in them, the other maps don't have this layer. I'm trying to add "roads" layer to all the maps that do not have this layer by using this code:

import arcpy,os,sys,fnmatch
from arcpy import env

env.workspace = r"G:\desktop\Project"
insertLayer = arcpy.mapping.Layer(r"G:\desktop\Project\layers\roads.lyr")
counter = 0 

for mxdname in arcpy.ListFiles("*.mxd"):
    print mxdname 
    mxd = arcpy.mapping.MapDocument(r"G:\desktop\Project\\" + mxdname)
    df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]
    refLayer = arcpy.mapping.ListLayers(mxd, "residence", df)[0]
for lyr in arcpy.mapping.ListLayers(mxd, "" ,df):
    if 'roads' not in lyr:  
        arcpy.mapping.InsertLayer(df, refLayer, insertLayer, "BEFORE") # BEFORE\ AFTER
mxd.save()
counter = counter + 1

del mxd 
print counter

and this is the error i get:

 >>> 
landUse.mxd
Traceback (most recent call last):
  File "G:/desktop/y/yaron/shonot/software/---gis---/tools/YARON_SCRIPTS/aaaaaaaaaaaaaaaaa.py", line 18, in <module>
if 'roads' not in lyr:
  File "C:\Program Files (x86)\ArcGIS\Desktop10.3\ArcPy\arcpy\arcobjects\mixins.py", line 361, in __iter__
self.layers
AttributeError: LayerObject: Get attribute layers does not exist
>>> 

UPDATE:

I added this code line:

  if 'roads' not in lyr.name:

and now 'roads' layer has been added several times (each map) to all maps no matter if they contain 'roads' layer or not.

Answer 1

Your variable lyr is a layer object and not a string or list of strings.

Consequently, to avoid that error you need to replace:

if 'roads' not in lyr:

with

if 'roads' not in lyr.name:

Answer 2

Rather than looping through the layers, you can use python's filter function to determine if the roads layer is present.

So, replace

for lyr in arcpy.mapping.ListLayers(mxd, "" ,df):
if 'roads' not in lyr:  
    arcpy.mapping.InsertLayer(df, refLayer, insertLayer, "BEFORE") # BEFORE\ AFTER

with

if not filter(lambda x: 'roads' in x.name, arcpy.mapping.ListLayers(mxd, "" ,df)):  
    arcpy.mapping.InsertLayer(df, refLayer, insertLayer, "BEFORE") # BEFORE\ AFTER

Update: If you don't want to use lambdas, you can set a flag in the loop then insert the layer afterwards

has_roads = False
for lyr in arcpy.mapping.ListLayers(mxd, "" ,df):
    if 'roads' in lyr.name:
        has_roads = True
if not has_roads:
    arcpy.mapping.InsertLayer(df, refLayer, insertLayer, "BEFORE") # BEFORE\ AFTER