Retrieve Retry-After on 429.

Hi all ! 

I'm trying in my API calls to handle limits.
And so on a 429 return code, I try to retrieve the "Retry-After" information
As mentioned in the help: https://developer.zendesk.com/api-reference/introduction/rate-limits/#monitoring-your-request-activity

Unfortunately, the returned header does not contain this information:

{'User-Agent': 'python-requests/2.21.0', 'Accept-Encoding': 'gzip, deflate', 'Accept': '*/*', 'Connection': 'keep-alive', 'Content-type': 'application/json', 'Content-Length': '134', 'Authorization': 'Basic xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx'}

And the returned json doesn't contain anything either.

Does anyone know where can i gets it?

Thanks !
Friendships,
Serge.