[Python-Dev] The current dict is not an "OrderedDict"

[Nathaniel Smith]

On Thu, Nov 9, 2017 at 1:46 PM, Cameron Simpson <cs at cskk.id.au> wrote:
> On 08Nov2017 10:28, Antoine Pitrou <solipsis at pitrou.net> wrote:
>>
>> On Wed, 8 Nov 2017 13:07:12 +1000
>> Nick Coghlan <ncoghlan at gmail.com> wrote:
>>>
>>> On 8 November 2017 at 07:19, Evpok Padding <evpok.padding at gmail.com>
>>> wrote:
>>> > On 7 November 2017 at 21:47, Chris Barker <chris.barker at noaa.gov>
>>> > wrote:
>>> >> if dict order is preserved in cPython , people WILL count on it!
>>> >
>>> > I won't, and if people do and their code break, they'll have only
>>> > themselves
>>> > to blame.
>>> > Also, what proof do you have of that besides anecdotal evidence ?
>>>
>>> ~27 calendar years of anecdotal evidence across a multitude of CPython
>>> API behaviours (as well as API usage in other projects).
>>>
>>> Other implementation developers don't say "CPython's runtime behaviour
>>> is the real Python specification" for the fun of it - they say it
>>> because "my code works on CPython, but it does the wrong thing on your
>>> interpreter, so I'm going to stick with CPython" is a real barrier to
>>> end user adoption, no matter what the language specification says.
>>
>>
>> Yet, PyPy has no reference counting, and it doesn't seem to be a cause
>> of concern.  Broken code is fixed along the way, when people notice.
>
>
> I'd expect that this may be because that would merely to cause temporary
> memory leakage or differently timed running of __del__ actions.  Neither of
> which normally affects semantics critical to the end result of most
> programs.

It's actually a major problem when porting apps to PyPy. The common
case is servers that crash because they rely on the GC to close file
descriptors, and then run out of file descriptors. IIRC this is the
major obstacle to supporting OpenStack-on-PyPy. NumPy is currently
going through the process to deprecate and replace a core bit of API
[1] because it turns out to assume a refcounting GC.

-n

[1] See:
  https://github.com/numpy/numpy/pull/9639
  https://mail.python.org/pipermail/numpy-discussion/2017-November/077367.html

-- 
Nathaniel J. Smith -- https://vorpus.org