inputLayer = r"...\testLayer.lyr"
targetLayerName = (arcpy.mapping.Layer(inputLayer)).name
fields = arcpy.ListFields(inputLayer)
lyrList = []
for item in fields:
    if ((item.name).split('.'))[0] not in lyrList:
        lyrList.append(((item.name).split('.'))[0])
for lyr in lyrList:
    if lyr != targetLayerName:
        print 'Join Layer: '+lyr