Repository navigation
pickle does not serialize Exception __cause__ field #73652
Description
Activity
diekhans commented
on Feb 6, 2017 diekhansmannequinMannequinAuthorpython3 pickle does not serialize the __cause__ field, as shown by the attached demo program.
True. Attributes __context__, __cause__ and __traceback__ are not pickled. The traceback objects are even not pickleable.
What is worse, some other non-special attributes are lost during pickling. For example name and path attributes of ImportError.
>>> try: import foo ... except Exception as ex: exc = ex ... >>> exc.name 'foo' >>> exc.__reduce__() (<class 'ModuleNotFoundError'>, ("No module named 'foo'",), {})
Or the value attribute of StopIteration if it was not passed to the constructor.
>>> exc = StopIteration() >>> exc.value = 42 >>> exc.__reduce__() (<class 'StopIteration'>, (), {})
kakshay21 commented
on Feb 16, 2019 kakshay21mannequinMannequinHey, can I work on this?
I get different output for Serhiy's first example now, but the same for the second:
>>> try: import foo ... except Exception as ex: exc = ex ... >>> exc.name 'foo' >>> exc.__reduce__() (<class 'ModuleNotFoundError'>, ("No module named 'foo'",), {'name': 'foo'}) >>> exc = StopIteration() >>> exc.value = 42 >>> exc.__reduce__() (<class 'StopIteration'>, ()) >>>
Attributes __context__, __cause__ and __traceback__ are not pickled. The traceback objects are even not pickleable.
It's not guaranteed that the __cause__ and __context__ are picklable either.
Should we try to pickle them, or should we document this and suggest traceback.TracebackException for storing or transmitting exception information?
Some stuff may be lost in time here, though for my benefit: Why don't the fields on exceptions go into
__dict__? If they were there wouldn't serialization work closer-to 'for free'?
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
Show more details
GitHub fields:
bugs.python.org fields: