code: def stringify(metrics_headers=()):
      
      metrics_headers = collections.OrderedDict(metrics_headers)
      return ' '.join(['%s/%s' % (k, v) for k, v in metrics_headers.items()])
docs: Convert the provided metrics headers to a string.
  
      Iterate over the metrics headers (a dictionary, usually ordered) and
      return a properly-formatted space-separated string
      (e.g. foo/1.2.3 bar/3.14.159).