[Python-Dev] [RFC] Removing pure Python implementation of OrderedDict

Eric Snow ericsnowcurrently at gmail.com
Tue Sep 5 13:13:59 EDT 2017

On Tue, Sep 5, 2017 at 1:38 AM, INADA Naoki <songofacandy at gmail.com> wrote:
> Like that, how about removing OrderedDict Pure Python implementation
> from stdlib and require it to implementation?


Like Antoine, I consider the pure Python implementation to be
valuable.  Furthermore, the pure Python implementation is the
reference, so its behavior is idiomatic.

> ### Thread safety
> AFAIK, there are no thread safety guarantee in OrderedDict.
> I don't look carefully, but some methods seems thread unsafe.

What isn't thread-safe?  I know that Raymond has a good understanding
of this area.  For instance, he was very clear about re-entrancy
concerns when I was working on the C implementation.  I recommend
getting feedback from him on this.  FWIW, I don't recall any bugs
related to thread-safety in OrderedDict, even though it's been around
a while.

> [snip]
> ### Less maintenance cost of test_ordered_dict.
> [snip]

I don't find this to be a strong argument.  If there are concerns with
the reference behavior then those should be addressed rather than used
to justify removing the implementation.

> ### `import collections` bit faster.
> [snip]

This is not a strong argument.  The difference is not significant
enough to warrant removing the reference implementation.

So, again, I'm against removing the pure Python implementation of
OrderedDict.  I highly recommend making sure you have Raymond's
cooperation before making changes in the collections module.


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