AttributeError with unicode object with data frame in python script

Question

I'm running a python script from arccatalog and it works, however, I am trying to add layers to an mxd and need to declare the data frame. I keep getting this error message.

type 'exceptions.AttributeError': 'unicode' object has no attribute '_arc_object' Failed to execute (StepByStep)

Selection of my code is below.

# Import arcpy module
import arcpy
import sys    

# Licenses
arcpy.CheckOutExtension("3D")    
arcpy.CheckOutExtension("spatial")    
arcpy.OverwriteOutput = True

# Script arguments
arcpy.env.extent = "E:\\School_Test\\SchoolTest.gdb\\Extent"    
arcpy.env.cellSize = "3"

mxd = arcpy.GetParameterAsText(0)    
arcpy.env.scratchWorkspace = arcpy.GetParameterAsText(1)    
arcpy.env.workspace = arcpy.GetParameterAsText(2)    
spRef = arcpy.GetParameterAsText(3)    
Survey_Data = arcpy.GetParameterAsText(4)    
Survey_X = arcpy.GetParameterAsText(5)    
Survey_Y = arcpy.GetParameterAsText(6)    
Survey_Z = arcpy.GetParameterAsText(7)    
Sample_Data = arcpy.GetParameterAsText(8)
Sample_X = arcpy.GetParameterAsText(9)    
Sample_Y = arcpy.GetParameterAsText(10)    
Selection_Criteria = arcpy.GetParameterAsText(11)    
Site_Grid = arcpy.GetParameterAsText(12)

df = arcpy.mapping.ListDataFrames(mxd, "Layers") [0]

Below this I declare variables then geoprocessing.

Any suggestions?

Answer 1

The problem with the code you have is that you are trying to convert an ArcMap Map Document into into a string and then you supply the string for the arcpy.mapping.ListDataFrames function. I usually handle this by:

1) Using the ArcMap Document data type for the input parameter.

2) Referring to the mxd file path as an Map Document object.

 mxd_raw = arcpy.GetParameterAsText(0) 
 mxd = arcpy.mapping.MapDocument(mxd_raw)

Your code after you've got access to the map document object could be:

mxd_raw = arcpy.GetParameterAsText(0)
mxd = arcpy.mapping.MapDocument(mxd_raw)
df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0]

for lyr in arcpy.mapping.ListLayers(mxd, "", df):
    arcpy.AddMessage(lyr.name)