code: def _sign_url(self, base_url, params, security_key):
          
          import hashlib
  
          if six.PY3:
              from urllib.parse import urlencode, quote, quote_plus
          else:
              from urllib import urlencode, quote, quote_plus
  
          if not base_url or not self.security_key:
              return None
  
          params = params.copy()
          address = params.pop('address')
  
          url = base_url + '?address=' + address + '&' + urlencode(params)
          encoded_url = quote(url, safe="/:=&?#+!$,;'@()*[]")
  
          signature = quote_plus(encoded_url + self.security_key).encode('utf-8')
          encoded_signature = hashlib.md5(signature).hexdigest()
  
          return encoded_signature
docs: Signs a request url with a security key.