code: def _conn_ready(self, conn):
          
          if ON_APP_ENGINE:
              # Google App Engine implementation of HTTPConnection doesn't contain
              # _HTTPConnection__response attribute. Moreover, it's not possible
              # to determine if given connection is ready. Reusing connections
              # simply doesn't make sense with App Engine urlfetch service.
              return False
          else:
              response = getattr(conn, '_HTTPConnection__response', None)
              return (response is None) or response.isclosed()
docs: There is a nice state diagram at the top of httplib.py.  It
          indicates that once the response headers have been read (which
          _mexe does before adding the connection to the pool), a
          response is attached to the connection, and it stays there
          until it's done reading.  This isn't entirely true: even after
          the client is done reading, the response may be closed, but
          not removed from the connection yet.
  
          This is ugly, reading a private instance variable, but the
          state we care about isn't available in any public methods.