AttributeError when pickling generic type annotations on Python 3.6

[pjwerneck]

I understand that type annotations are not supported for Python 3.6, but I'm getting an AttributeError for abc._get_dump when pickling generic type annotations.

• Python 3.6.8
• cloudpickle 1.3.0:

  File "/home/pedro/.virtualenvs/KZG8XYVK/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 899, in save_global
    self.save_dynamic_class(obj)
  File "/home/pedro/.virtualenvs/KZG8XYVK/lib/python3.6/site-packages/cloudpickle/cloudpickle.py", line 642, in save_dynamic_class
    (registry, _, _, _) = abc._get_dump(obj)
AttributeError: module 'abc' has no attribute '_get_dump'

Here's a minimal example to reproduce the error:

import typing
import cloudpickle

X = typing.TypeVar("X")

class Input(typing.Generic[X]):
    pass

class Lero:
    a: Input[int]

obj = Lero()

cloudpickle.dumps(obj)

My workaround for it was patching the abc module with a copy of the pure Python implementation of _get_dump at https://github.com/python/cpython/blob/3.7/Lib/test/libregrtest/refleak.py#L8

try:
    import abc
    abc._get_dump
except AttributeError:
    import weakref

    def _get_dump(cls):
        # Reimplement _get_dump() for pure-Python implementation of
        # the abc module (Lib/_py_abc.py)
        registry_weakrefs = set(weakref.ref(obj) for obj in cls._abc_registry)
        return (registry_weakrefs, cls._abc_cache,
                cls._abc_negative_cache, cls._abc_negative_cache_version)
    abc._get_dump = _get_dump

[pierreglaser]

Thank you very much for the compact reproducer. I'll investigate.