code: def getTopdir(topfile, start=None):
      
      if not start:
          start = os.getcwd()
      here = start
      toomany = 20
      while toomany > 0:
          if os.path.exists(os.path.join(here, topfile)):
              return here
          next = os.path.dirname(here)
          if next == here:
              break                       # we've hit the root
          here = next
          toomany -= 1
      output("Unable to find topfile '{}' anywhere "
             "from {} upwards".format(topfile, start))
      sys.exit(1)
docs: walk upwards from the current directory until we find this topfile