code: def get_trace_id():
      
      checkers = (
          get_trace_id_from_django,
          get_trace_id_from_flask,
          get_trace_id_from_webapp2,
      )
  
      for checker in checkers:
          trace_id = checker()
          if trace_id is not None:
              return trace_id
  
      return None
docs: Helper to get trace_id from web application request header.
  
      :rtype: str
      :returns: TraceID in HTTP request headers.