STINNER Victor <[email protected]> added the comment:
PR 20960 (_bz2 module) triggers an interesting question. The effect of
converting a static type to a heap type on pickle, especially for protocols 0
and 1.
pickle.dumps(o, 0) calls object.__reduce__(o) which calls copyreg._reduce_ex(o,
0).
copyreg._reduce_ex() behaves differently on heap types:
...
for base in cls.__mro__:
if hasattr(base, '__flags__') and not base.__flags__ & _HEAPTYPE:
break
else:
base = object # not really reachable
...
There are 3 things which impacts serialization/deserialization:
- Py_TPFLAGS_HEAPTYPE flag in the type flags
- Is __new__() overriden in the type?
- Py_TPFLAGS_BASETYPE flag in the type flags
Examples:
* In Python 3.7, _random.Random() cannot be serialized because it's a static
type (it doesn't have (Py_TPFLAGS_HEAPTYPE)
* In master, _random.Random() cannot be deserialized because _random.Random()
has __new__() method (it's not object.__new__())
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<https://bugs.python.org/issue40077>
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