Yes, but that could also be said about ordinary global classes.
if sys.args[1] == "a":
class A:
pass
a = A()
print(pickle.dumps(a))
else:
a = pickle.loads(input()) # no definition of class A in this run
> I'm not sure that would work in practice. If I pickle Local_here, then
> run a new instance of the program that loads in the pickle file, but
> has never even run f() in the new instance, then the class Local
> doesn't exist. So you can't unpikcle an instance of it, as you don't
> know how to create the class...
>
> Apologies if I'm misunderstanding your point here, but it feels like
> what you're proposing would only work if you pickled and unpickled the
> data in the *same* running instance of the program.
>
> Paul
>
On Thu, 3 Sep 2020 at 18:06, haael <[email protected]> wrote:
Only objects of globally defined classes are picklable:
class Global:
pass
picklable = Global()
def f():
class Local:
pass
return Local
Local_here = f()
unpicklable = Local_here()
However, instances become picklable if we assign the local class to some
globally reachable identifier.
Local_here.__qualname__ = 'Local_here'
now_picklable = Local_here()
Why not make it a feature? Let's define module level global identifier,
for instance `__local_classes__`. It will be a weak dictionary of class
objects. Whenever a local class is created, a weak ref is made and
reflected in the new classes' qualname.
def f():
class Local:
pass
# weak ref is created with some unique id
return Local
Local_here = f()
print(Local_here.__qualname__) # '__local_classes__["uniqueidxxx"]'
assert Local_here is __local_classes__["uniqueidxxx"]
Likewise for local functions.
This would make many objects picklable, which also positively affects
modules that rely on `pickle`, like `multiprocessing`.
_______________________________________________
Python-ideas mailing list -- [email protected]
To unsubscribe send an email to [email protected]
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/[email protected]/message/KJY74GM24SS7S7ZAWYJTSTLAUL2SCJVC/
Code of Conduct: http://python.org/psf/codeofconduct/
