code: def infer_bulk_complete_from_fs(datetimes, datetime_to_task, datetime_to_re):
      
      filesystems_and_globs_by_location = _get_filesystems_and_globs(datetime_to_task, datetime_to_re)
      paths_by_datetime = [[o.path for o in flatten_output(datetime_to_task(d))] for d in datetimes]
      listing = set()
      for (f, g), p in zip(filesystems_and_globs_by_location, zip(*paths_by_datetime)):  # transposed, so here we're iterating over logical outputs, not datetimes
          listing |= _list_existing(f, g, p)
  
      # quickly learn everything that's missing
      missing_datetimes = []
      for d, p in zip(datetimes, paths_by_datetime):
          if not set(p) <= listing:
              missing_datetimes.append(d)
  
      return missing_datetimes
docs: Efficiently determines missing datetimes by filesystem listing.
  
      The current implementation works for the common case of a task writing
      output to a ``FileSystemTarget`` whose path is built using strftime with
      format like '...%Y...%m...%d...%H...', without custom ``complete()`` or
      ``exists()``.
  
      (Eventually Luigi could have ranges of completion as first-class citizens.
      Then this listing business could be factored away/be provided for
      explicitly in target API or some kind of a history server.)