docs: def extract_stack(f=None, limit=None):
      """equivalent to traceback.extract_stack(), but also works with psyco
      """
      if f is not None:
          raise RuntimeError("Timba.utils.extract_stack: f has to be None, don't ask why")
      # normally we can just use the traceback.extract_stack() function and
      # cut out the last frame (which is just ourselves). However, under psyco
      # this seems to return an empty list, so we use sys._getframe() instead
      lim = limit
      if lim is not None:
          lim += 1
      tb = traceback.extract_stack(None, lim)
      if tb:
          return tb[:-1];  # skip current frame
      # else presumably running under psyco
      return nonportable_extract_stack(f, limit)