Description
In the Python implementation of pickle
setting some handlers to None causes a fallback to other methods.
- Setting
Pickler.reducer_override
to None has the same effect as not setting this attribute -- falling back to other methods. - Setting the
dispatch_table
to None leads to falling back to__reduce_ex__
. - Setting the
__reduce_ex__
attribute to None leads to falling back to__reduce__
. - Setting the
__setstate__
attribute to None leads to falling back to the default implementation of__setstate__
(setting__dict__
and slots).
In the C implementation all this leads to TypeError: 'NoneType' object is not callable
.
The copy
module follows the Python implementation of pickle
, except that it fails for any false value of __reduce__
, not just None.
In most other code setting a dunder method to None leads to a TypeError (either raise explicitly or just generic "'NoneType' object is not callable").
We should decide what behavior should be in the pickle
and copy
module. On one hand, the Python implementation was primary. On other hand, it was inconsistent between the pickle
and copy
modules and was already changed in the past, the C implementation of pickle
is now used by most users, and it is more consistent with other code.
See also:
https://mail.python.org/archives/list/python-dev@python.org/thread/YGAK34DRWJFSIV2VZ4NC2J24XO37GCMM/
https://docs.python.org/3.10/reference/datamodel.html#id2
#70146
#55781
#60755
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