Header Ordering

In unusual circumstances you may want to provide headers in an ordered manner. If you pass an OrderedDict to the headers keyword argument, that will provide the headers with an ordering. However, the ordering of the default headers used by Requests will be preferred, which means that if you override default headers in the headers keyword argument, they may appear out of order compared to other headers in that keyword argument.

If this is problematic, users should consider setting the default headers on a Session object, by setting Session to a custom OrderedDict. That ordering will always be preferred.