Re: Method __func__ objects are unpicklable

This is not just about the content of the name attributes: ;bound methods
do contain a reference to the specific instance
they are bound too - which is not retrievable (or maybe is through some
dunder attribute) - this instance has to be pickled, transported
and its reference updated on unpickling.

On Fri, Jun 10, 2022 at 9:00 AM haael <[email protected]> wrote:

>
>
> During some sophisticated pickling I noticed that method `__func__`
> objects are unpicklable, because they share the name with the bound
> method object itself.
>
>
> ```
> from pickle import dumps
>
> class A:
>      @classmethod
>      def b(cls):
>          pass
>
> print(A.b) # <bound method A.b of <class '__main__.A'>>
> print(A.b.__func__) # <function A.b at 0x7f5574570bf8>
>
> dumps(A.b) # works
> dumps(A.b.__func__) # breaks
> # >Traceback (most recent call last):
> # >  File "<stdin>", line 1, in <module>
> # >_pickle.PicklingError: Can't pickle <function A.b at 0x7fd1d50d8bf8>:
> # >it's not the same object as __main__.A.b
> ```
>
>
> The last call compains that global symbol "A.b" is not the same object
> as `A.b.__func__`.
>
> Everything would work if the `__func__` objects had the suffix
> ".__func__" in their qualname.
>
> Actually setting the qualname of the `__func__` object makes it
> picklable, but then the bound method object is unpicklable, as it
> inherits the name from the `__func__`. It would be good if they were
> separate.
>
> This is an attempt at emulating the desired behavior:
>
>
> ```
> from pickle import dumps
>
> class A:
>      pass
>
> def c(cls):
>      pass
>
> A.c = lambda: c(A)
> A.c.__qualname__ = "A.c"
> A.c.__name__ = "c"
> A.c.__self__ = A
> A.c.__func__ = c
> A.c.__func__.__qualname__ = "A.c.__func__"
>
> print(A.c) # <function A.c at 0x7f83ceabcbf8>
> print(A.c.__func__) # <function A.c.__func__ at 0x7f83ceabcb70>
>
> dumps(A.c) # works
> dumps(A.c.__func__) # works
> ```
>
>
> Can we make the `__func__` objects picklable this way?
>
>
> haael
>
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