arcgis desktop - Adding shapefile as layer in ArcMap via Python scripting?

I am trying to automate various tasks in ArcGIS Desktop (using ArcMap generally) with Python, and I keep needing a way to add a shapefile to the current map. (And then do stuff to it, but that's another story).

The best I can do so far is to add a layer file to the current map, using the following ("addLayer" is a layer file object):

def AddLayerFromLayerFile(addLayer): 
  import arcpy 
  mxd = arcpy.mapping.MapDocument("CURRENT") 
  df = arcpy.mapping.ListDataFrames(mxd, "Layers")[0] 
  arcpy.mapping.AddLayer(df, addLayer, "AUTO_ARRANGE") 
  arcpy.RefreshActiveView() 
  arcpy.RefreshTOC() 
  del mxd, df, addLayer 

However, my raw data is always going be shapefiles, so I need to be able to open them. (Equivantly: convert a shapefile to a layer file without opening it, but I'd prefer not to do that).