code: def _parse_wsgi_headers(wsgi_environ):
          
          prefix = 'HTTP_'
          p_len = len(prefix)
          # use .items() despite suspected memory pressure bc GC occasionally
          # collects wsgi_environ.iteritems() during iteration.
          headers = {
              key[p_len:].replace('_', '-').lower():
                  val for (key, val) in wsgi_environ.items()
              if key.startswith(prefix)}
          return headers
docs: HTTP headers are presented in WSGI environment with 'HTTP_' prefix.
          This method finds those headers, removes the prefix, converts
          underscores to dashes, and converts to lower case.
  
          :param wsgi_environ:
          :return: returns a dictionary of headers