fails to pickle @dataclass instances

[mmckerns]

Originally reported in: uqfoundation/klepto#71

>>> import dill
>>> from dataclasses import dataclass
>>> @dataclass (frozen=True)
... class Foo:
...     name : str
... 
>>> foo = Foo (name='dill')
>>> 
>>> dill.dumps(foo)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 294, in dumps
    dump(obj, file, protocol, byref, fmode, recurse)#, strictio)
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 287, in dump
    pik.dump(obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 437, in dump
    self.save(obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 633, in save_reduce
    save(cls)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 1312, in save_type
    obj.__bases__, _dict), obj=obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 638, in save_reduce
    save(args)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 786, in save_tuple
    save(element)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 899, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 899, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 887, in _batch_setitems
    save(v)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 549, in save
    self.save_reduce(obj=obj, *rv)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 662, in save_reduce
    save(state)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 771, in save_tuple
    save(element)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 899, in save_module_dict
    StockPickler.save_dict(pickler, obj)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 856, in save_dict
    self._batch_setitems(obj.items())
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 882, in _batch_setitems
    save(v)
  File "/opt/local/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pickle.py", line 504, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Users/mmckerns/lib/python3.7/site-packages/dill-0.3.0.dev0-py3.7.egg/dill/_dill.py", line 1145, in save_dictproxy
    raise ReferenceError("%s does not reference a class __dict__" % obj)
ReferenceError: {} does not reference a class __dict__
>>> 

[lazylynx]

Is there any progress about this?
It seems that this issue caused by considering metadata of dataclasses.field as DictProxyType not MappingProxyType.

[tvalentyn]

#324 may be related.

[tvalentyn]

This appears to be fixed at master.

[mmckerns]

Confirmed. This is also fixed due to #324

Python 3.7.4 (default, Sep  7 2019, 20:47:14) 
[Clang 9.0.0 (clang-900.0.39.2)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import dill
>>> from dataclasses import dataclass
>>> @dataclass(frozen=True)
... class Foo:
...   name:str
... 
>>> foo = Foo(name='dill')
>>> dill.copy(foo)
Foo(name='dill')
>>>