[Python-Dev] PEP 455: TransformDict (original) (raw)

R. David Murray rdmurray at bitdance.com
Tue Oct 8 21:19:48 CEST 2013

On Tue, 08 Oct 2013 22:02:43 +0400, Yuriy Taraday <yorik.sar at gmail.com> wrote:

There should be a way to avoid creation of the second dict when there is no need to store original keys. For example, email.message module doesn't store original headers as they are not needed. The same applies to web frameworks parsing HTTP headers or WSGI environment.

This is not true. email.message very carefully preserves the original header name, case and all [*], that's part of its mandate (faithfully reproducing the original parsed message).

That said, email.message can't use transformdict, since email.message needs a list-with-case-insensitive-keyed-lookup, not a dict, because it also preserves the original order of the headers. And it couldn't use an orderedtransformdict, either, since it also has to preserve duplicate headers.

--David

[*] currently it loses whitespace information in certain cases, but the new header parser/folder is supposed to fix that...or will once I fix a few more corner cases :)

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