docs: def checksum(symbol, doc):
      """
      Checksum the passed in dictionary
      """
      sha = hashlib.sha1()
      sha.update(symbol.encode('ascii'))
      for k in sorted(iter(doc.keys()), reverse=True):
          v = doc[k]
          if isinstance(v, six.binary_type):
              sha.update(doc[k])
          else:
              sha.update(str(doc[k]).encode('ascii'))
      return Binary(sha.digest())