code: def _build_raw_headers(self, headers: Dict) -> Tuple:
          
          raw_headers = []
          for k, v in headers.items():
              raw_headers.append((k.encode('utf8'), v.encode('utf8')))
          return tuple(raw_headers)
docs: Convert a dict of headers to a tuple of tuples
  
          Mimics the format of ClientResponse.