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1.1.3 Response Objects

Response objects are derived from `dict` and map header names (lower case with the trailing colon removed) to header values. In addition to the dict methods a Response object also has:

`fromcache`
  If `true` the the response was returned from the cache.

`version`
  The version of HTTP that the server supports. A value of 11 means '1.1'.

`status`
  The numerical HTTP status code returned in the response.

`reason`
  The human readable component of the HTTP response status code.

`previous`
  If redirects are followed then the `Response` object returned is just for the very last HTTP request and previous points to the previous `Response` object. In this manner they form a chain going back through the responses to the very first response. Will be `None` if there are no previous respones.

The Response object also populates the header `content-location`, that contains the URI that was ultimately requested. This is useful if redirects were encountered, you can determine the ultimate URI that the request was sent to. All Response objects contain this key value, including `previous` responses so you can determine the entire chain of redirects. If `Http.force_exception_to_status_code` is `True` and the number of redirects has exceeded the number of allowed number of redirects then the `Response` object will report the error in the status code, but the complete chain of previous responses will still be in tact.