This is the solution I used in the end
desc = arcpy.Describe(Templatelayer)
arcpy.CreateFishnet_management(Grid_layer,str(desc.extent.lowerLeft),str(desc.extent.XMin) + " " + str(desc.extent.YMax),"2","2",None,None,str(desc.extent.upperRight),"NO_LABELS","#","POLYGON")
. Thank you for your help