Requests might but that's irrelevant. Requests is built on top of urllib3 which is built on top of httplib which does use a plain dict. Also the relevant RFC says order is irrelevant.
The order in which header fields with differing field names are received is not significant. However, it is "good practice" to send general-header fields first, followed by request-header or response-header fields, and ending with the entity-header fields.
Yes, if you're implementing a client or server, you should not depend on the order of the headers. Completely separately, when I have a command line client for debugging, I want to see the request and response exactly as they were sent/received, respectively.
> Instances of the same path and name will overwrite each other, with the latest instance taking precedence. Instances of the same path but different names will add additional mappings.
> When sending cookies to a server, all cookies with a more specific path mapping should be sent before cookies with less specific path mappings. For example, a cookie "name1=foo" with a path mapping of "/" should be sent after a cookie "name1=foo2" with a path mapping of "/bar" if they are both to be sent.
