code: def parse_session_token(response_headers):
          
  
          # extract session token from response header
          session_token = ''
          if http_constants.HttpHeaders.SessionToken in response_headers:
                  session_token = response_headers[http_constants.HttpHeaders.SessionToken]
  
          id_to_sessionlsn = {}
          if session_token is not '':
              ''' extract id, lsn from the token. For p-collection,
              the token will be a concatenation of pairs for each collection'''
              token_pairs = session_token.split(',')
              for token_pair in token_pairs:
                  tokens = token_pair.split(':')
                  if (len(tokens) == 2):
                      id = tokens[0]
                      sessionToken = VectorSessionToken.create(tokens[1])
                      if sessionToken is None:
                          raise HTTPFailure(http_constants.StatusCodes.INTERNAL_SERVER_ERROR, "Could not parse the received session token: %s" % tokens[1])
                      id_to_sessionlsn[id] = sessionToken
          return id_to_sessionlsn
docs: Extracts session token from response headers and parses
  
          :param dict response_headers:
  
          :return:
              A dictionary of partition id to session lsn
              for given collection 
          :rtype: dict