[issue21333] Document recommended exception for objects that shouldn't be pickled
New submission from Stefan Schwarzer:
I recently was confused whether to raise a `PicklingError` or `TypeError` in `__getstate__` if objects of my class can't and shouldn't be pickled. [1]
Terry Reedy advised I should use `TypeError`. [2]
I wonder if the `pickle` module documention should explicitly recommend using `TypeError` if a class wants to say that its objects can't be pickled. What do you think?
[1] https://mail.python.org/pipermail/python-list/2014-April/670987.html
[2] https://mail.python.org/pipermail/python-list/2014-April/671002.html
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assignee: docs@python
components: Documentation
messages: 217054
nosy: docs@python, sschwarzer
priority: normal
severity: normal
status: open
title: Document recommended exception for objects that shouldn't be pickled
type: enhancement
versions: Python 3.5
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Python tracker
Changes by Berker Peksag
Michael Crouch added the comment:
When pickling an object fails on line 70 of copy_reg.py, a "TypeError" is raised. However, according to section 11.1.3 of the Standard Library documentation, when an unpicklable object is passed to the dump() method the "PicklingError" exception will be raised.
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components: +Library (Lib) -Documentation
nosy: +Michael Crouch
versions: +Python 2.7 -Python 3.5
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Python tracker
Serhiy Storchaka added the comment:
PicklingError is raised in following cases:
1. Programmical Pickler error (Pickler.__init__() was not called by subclass' __init__()).
2. Due to protocol or implementation limitations: memoizing more than 2**32 objects, saving non-ASCII globals with protocol < 3, etc. Exception type is implementation depended. Sometimes OverflowError or struct.error can be raised instead.
3. When __reduce__/__reduce_ex__ returns invalid value: neither str or tuple, a tuple has wrong size, first tuple element is not a callable, first argument for __newobj__/__newobj_ex__ has no __new__ or doesn't match a type of pickled object, global lookup is failed or doesn't match pickled object, etc.
4. When extension code is not an integer or out of range.
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nosy: +serhiy.storchaka
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Python tracker
Terry J. Reedy
participants (5)
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Berker Peksag -
Michael Crouch
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Serhiy Storchaka
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Stefan Schwarzer
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Terry J. Reedy