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

INADA Naoki songofacandy at gmail.com
Tue Sep 5 09:19:18 EDT 2017 
On Tue, Sep 5, 2017 at 8:48 PM, Serhiy Storchaka <storchaka at gmail.com> wrote:
> 05.09.17 11:38, INADA Naoki пише:
>>
>> ## Cons
>>
>> * All Python 3.7 implementations should provide _collections.OrderedDict
>>    PyPy has it already.  But I don't know about micropython.
>
>
> Current C implementation of OrderedDict is not safe regarding using mutating
> dict methods (or dict C API) like dict.__setitem__ or PyDict_SetItem. Using
> them can cause hangs or segfaults. See issue24726 and issue25410. I hope
> your implementation will solve these issues, but there may be others.

Thanks for sharing these issues.
My pull request is still early stage and may have some bugs.
But I think it will solve many of issues because most odd behaviors comes from
difficult of consistency between linked list and dict.

> While
> the C implementation still is not enough mature, we should allow users that
> encountered one of such issues to use pure Python implementation which is
> free from hangs and segfaults.
>

I see.
Maybe, we can move Pure Python OrderedDict to collections._odict module,
and collections/__init__.py can be like this:

    from _collections import OrderedDict
    # Pure Python implementation can be used when C implementation
cause segfault.
    # from collections._odict import OrderedDict


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