[Python-Dev] Guarantee ordered dict literals in v3.7? (original) (raw)

Stefan Krah stefan at bytereef.org
Sun Nov 5 13:39:31 EST 2017

On Sun, Nov 05, 2017 at 01:14:54PM -0500, Paul G wrote:

I'm not entirely sure I understand the full set of reasoning for this - I couldn't really tell what the problem with OrderedDict is from the link Stefan provided. It seems to me like a kind of huge change for the language to move from arbitrary-ordered to guaranteed-ordered dict. The problem I see is that this introduces a huge backwards compatibility burden on all implementations of Python.

Scientific applications want something like

{'a': 10, 'b': "foo", 'c': {'this': b'123'}}

as an ordered initializer for unboxed or typed (or both) data. In general, if dicts are ordered, they can be used for example as initializers for (nested) C structs.

2. Someone invents a new arbitrary-ordered container that would improve on the memory and/or CPU performance of the current dict implementation

I would think this is very unlikely, given that the previous dict implementation has always been very fast. The new one is very fast, too.

Stefan Krah

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