>>> import dill
>>> from dill._objects import failures, registered, succeeds
>>> import warnings
>>> warnings.filterwarnings('ignore')
>>> def check(d, ok=True):
...   res = []
...   for k,v in d.items():
...     try:
...       z = dill.copy(v)
...       if ok: res.append(k)
...     except:
...       if not ok: res.append(k)
...   return res
... 
>>> check(failures)
[]
>>> check(registered, ok=False) # should be empty
['SymtableEntryType']
>>> check(succeeds, ok=False) # should be empty
['SymtableEntryType']
>>> 
>>> import builtins
>>> import types
>>> q = dill._dill._reverse_typemap
>>> p = {k:v for k,v in q.items() if k not in vars(builtins) and k not in vars(types)}
>>> set(p.keys()).difference(registered.keys())
set()
>>> set(registered.keys()).difference(p.keys())
set()
>>>