realead <[email protected]> added the comment:
This change makes life harder for people trying to get sane behavior with sets
for float-, complex- and tuple-objects containing NaNs. With "sane" meaning,
that
set([nan, nan, nan]) => {nan}
Until now, one has only to override the equal-comparison for these types but
now also hash-function needs to be overriden (which is more complicated e.g.
for tuple).
----------------------------------------------------------------
On a more abstract level: there are multiple possible equivalence relations.
The one used right now for floats is Py_EQ and results in
float("nan)!=float("nan") due to IEEE 754.
In hash-set/dict we would like to use an equivalence relation for which all
NaNs would be in the same equivalence class. Maybe a new comparator is called
for (like PY_EQ_FOR_HASH_COLLECTION), which would yield float("nan") equivalent
to float("nan") and which should be used in hash-set/dict?
----------
nosy: +realead
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Python tracker <[email protected]>
<https://bugs.python.org/issue43475>
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