Adding feature class to TOC using ArcPy? [duplicate]

Question

This question has been asked multiple times with proper answers:

• How to add feature class to MXD with ArcPy (Python)?
• Adding shapefile or feature class as layer in ArcGIS Desktop using Python/ArcPy?
• Adding feature class into ArcGIS 10.3 mxd using python script

but I still cannot get it right.

I am using ArcGIS 10.2.2.

I want to add via a Python standalone script a Featureclass from a file-gdb to the TOC. If I try it in the ArcGIS Python window it works fine. However in a standalone script nothing happens. There is no error message or anything. I already thought it might be a bug, but it seems to work for everyone else. I also tried it with a .lyr and it didn´t work either. Someone got a hint for me?

Here is the code (I also tried the one from the ArcGIS help site, and from all the links above).

import arcpy
mxd = arcpy.mapping.MapDocument(r"C:\GIS\KUP\Check.mxd")
df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
addLayer = arcpy.mapping.Layer(r"C:\GIS\KUP\Ergebnisse.gdb\Potenziale_singlepart_final")
arcpy.mapping.AddLayer(df, addLayer, "BOTTOM")

I also tried :

addLayer = arcpy.mapping.Layer(r"C:\GIS\KUP\Potenziale_singlepart_final.lyr")

What am I doing wrong? I am trying for a week now. I`m getting crazy with this one. Seems so easy.

Answer 1

On the code snippet and symptoms presented in the question:

import arcpy
mxd = arcpy.mapping.MapDocument(r"C:\GIS\KUP\Check.mxd")
df = arcpy.mapping.ListDataFrames(mxd, "*")[0]
addLayer = arcpy.mapping.Layer(r"C:\GIS\KUP\Ergebnisse.gdb\Potenziale_singlepart_final")
arcpy.mapping.AddLayer(df, addLayer, "BOTTOM")

it seems to me, like @MichaelMilesStimson has commented, that you are missing the line of code at the end which is necessary to persist any changes made to the MXD you open as a Map Document object:

mxd.save()

or, if you prefer:

mxd.saveACopy (file_name, {version})