[Web-SIG] Why is response_headers a list instead of a dict?

[Clark C. Evans]

Why is response_headers a list instead of a dict?

>From RFC 2616 Section 4.2:

    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.

    Multiple message-header fields with the same field-name MAY be
    present in a message if and only if the entire field-value for that
    header field is defined as a comma-separated list [i.e., #(values)].
    It MUST be possible to combine the multiple header fields into one
    "field-name: field-value" pair, without changing the semantics of
    the message, by appending each subsequent field-value to the first,
    each separated by a comma. 

In other words: (a) order does not matter, (b) it is reasonable to
restrict a header field to a single (header_name, header_value) pair.
Indeed, according to the specification, a HTTP Proxy could re-arrange
headers and condense N headers of the same type by simply concatenating
their values with a comma.

I'm asking this because it is quite painful (and very much an unnecessary 
pain) to work with headers in complex WSGI-based middleware applications.

Kind Regards,

Clark