code: def get_signature_string(params, secret):
      
      str_list = [str(item) for item in extract_params(params)]
      str_list.sort()
      return (secret + ''.join(str_list)).encode('utf-8')
docs: Returns the unhashed signature string (secret + sorted list of param values) for an API call.
      @param params: dictionary values to generate signature string
      @param secret: secret string