Re: Migrating to BTrees 4.x

On 11/20/16 9:31 AM, Jim Fulton wrote:
>
>
> On Sun, Nov 20, 2016 at 12:11 PM, Jason Madden 
> <[email protected] <mailto:[email protected]>> 
> wrote:
>
>
>     > On Nov 20, 2016, at 10:25, Jim Fulton <[email protected]
>     <mailto:[email protected]>> wrote:
>     >
>     >> But it seems safe to say there are at least some discrepancies
>     and some clear bugs in the handling of unorderable objects still.
>     >
>     > Yup.  Partly I suspect this is the related to the many ways one
>     can express comparison in Python. (Talk about more than one way to
>     do it.)
>     >
>     > I think this may also be related to inserting into an empty
>     BTree, where there's noting to compare the new item to and thus no
>     opportunity to fail.  Perhaps, if we're paranoid, we should
>     compare the first item to itself on insert.
>
>     You're right, under Python 3, this only happens in an empty tree.
>     Once there are other items, you get "TypeError: unorderable types:
>     Bad() < ..." errors. Under Python 2, of course, no such luck.
>
>     > In any case, I think the focus for this seat belt should be on
>     insertion.
>
>     I've opened a series of issues in the repository
>     (https://github.com/zopefoundation/BTrees/issues
>     <https://github.com/zopefoundation/BTrees/issues>) that I think
>     capture the discussion here.
>
>
> Thanks.
>
>     I may be able to come up with some PRs over the next week for them.
>
>
> It looks like David was going to try a fix. David, did this discussion 
> help?

I finally had time to look at this again today. I've got a branch 
(check-obj-cmp-on-insert-only) that makes the CPython implementation 
only do the check on insertion so it's more like the Python 
implementation. However, trying to delete None as a key still raises 
"TypeError: unorderable types: NoneType() < NoneType()" in Python 3 
(both implementations; we weren't testing the pure-Python implementation 
on Python 3 except for PyPy3). This is presumably Python itself 
complaining when trying to search for the bucket. I suppose the 
workaround is: for the search during delete only, if the keys use 
default comparison, compare them using a function that mimics Python 2 
comparison and thus skips the check for unorderable types. Gaaa...

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