dill fails to pickle attrs-created classes #411
Description
It seems that dill is doing something that breaks pickling of attrs-created classes. Here is an MWE that shows that dill.dumps fails where pickle.dumps would succeed:
import attr
import dill
import pickle
@attr.s
class A:
a = attr.ib()
if __name__ == "__main__":
v = A(1)
print(f"Pickling {v}")
print(pickle.dumps(v))
print(f"Dill pickling {v}")
print(dill.dumps(v))Here is the result, with traceback:
Details
Pickling A(a=1)
b'\x80\x04\x95\x1f\x00\x00\x00\x00\x00\x00\x00\x8c\x08__main__\x94\x8c\x01A\x94\x93\x94)\x81\x94}\x94\x8c\x01a\x94K\x01sb.'
Dill pickling A(a=1)
Traceback (most recent call last):
File "/tmp/tmp.sQU1rFY7Ax/mwe.py", line 17, in <module>
print(dill.dumps(v))
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 273, in dumps
dump(obj, file, protocol, byref, fmode, recurse, **kwds)#, strictio)
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 267, in dump
Pickler(file, protocol, **_kwds).dump(obj)
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 454, in dump
StockPickler.dump(self, obj)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 487, in dump
self.save(obj)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 603, in save
self.save_reduce(obj=obj, *rv)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 687, in save_reduce
save(cls)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 560, in save
f(self, obj) # Call unbound method with explicit self
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 1373, in save_type
pickler.save_reduce(_create_type, (type(obj), obj.__name__,
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 692, in save_reduce
save(args)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 560, in save
f(self, obj) # Call unbound method with explicit self
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 901, in save_tuple
save(element)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 560, in save
f(self, obj) # Call unbound method with explicit self
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 941, in save_module_dict
StockPickler.save_dict(pickler, obj)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 971, in save_dict
self._batch_setitems(obj.items())
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 997, in _batch_setitems
save(v)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 603, in save
self.save_reduce(obj=obj, *rv)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 687, in save_reduce
save(cls)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 560, in save
f(self, obj) # Call unbound method with explicit self
File "/tmp/tmp.sQU1rFY7Ax/venv/lib/python3.9/site-packages/dill/_dill.py", line 1390, in save_type
StockPickler.save_global(pickler, obj, name=name)
File "/home/nlx5/.pyenv/versions/3.9.4/lib/python3.9/pickle.py", line 1070, in save_global
raise PicklingError(
_pickle.PicklingError: Can't pickle <class 'AAttributes'>: it's not found as builtins.AAttributes
I believe the issue has something to do with the way dill is trying to save the attrs-created class. It runs up against this ad-hoc class created with eval and breaks. I am not sure why pickle doesn't have this problem.
I have tested this with several attrs versions between 18.2.0 and 21.2.0, as well as with dill versions going back to 0.2.5, and all versions are affected.