Bad exceptions from pickle

[bobalex]

BPO	504723
Nosy	@loewis, @nascheme

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2002-03-22.22:18:14.000>
created_at = <Date 2002-01-17.03:55:22.000>
labels = ['invalid', 'library']
title = 'Bad exceptions from pickle'
updated_at = <Date 2002-03-22.22:18:14.000>
user = 'https://bugs.python.org/bobalex'

bugs.python.org fields:

activity = <Date 2002-03-22.22:18:14.000>
actor = 'nascheme'
assignee = 'none'
closed = True
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2002-01-17.03:55:22.000>
creator = 'bobalex'
dependencies = []
files = []
hgrepos = []
issue_num = 504723
keywords = []
message_count = 4.0
messages = ['8819', '8820', '8821', '8822']
nosy_count = 4.0
nosy_names = ['loewis', 'nascheme', 'bobalex', 'tchristopher']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = None
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue504723'
versions = ['Python 2.2']

[bobalex]

Here is an annotated session that shows some incorrect
exceptions raised with bad input. I'm assuming that it
is intended that when attempting to load a pickle file,
we should only have to check for UnpicklingError, not
for several other possible exceptions.

>>> import sys
>>> sys.version
'2.2 (#1, Dec 26 2001, 16:14:13) \n[GCC 2.96 20000731
(Mandrake Linux 8.1 2.96-0.62mdk)]'

Problem 1: Attempting to load an empty file produces an
EOFError exception, but should probably produce an
UnpicklingError exception. This happens with both
pickle and cPickle.

>> import cPickle as pickle
>> import pickle as pk

>>> f=open("/dev/null")     # Empty file
>>> ff=StringIO("asdfasdfasdfasdfasdfasdf")   # Garbage
file

>>> pickle.load(f)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
EOFError

>>> pk.load(f)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.2/pickle.py", line 977, in
load
    return Unpickler(file).load()
  File "/usr/lib/python2.2/pickle.py", line 592, in
load
    dispatch[key](self)
  File "/usr/lib/python2.2/pickle.py", line 606, in
load_eof
    raise EOFError
EOFError

Problem 2: With cPickle, loading a garbage file
produced and IndexError, not an Unpickling error.

>>> pk.load(ff)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
  File "/usr/lib/python2.2/pickle.py", line 977, in
load
    return Unpickler(file).load()
  File "/usr/lib/python2.2/pickle.py", line 592, in
load
    dispatch[key](self)
  File "/usr/lib/python2.2/pickle.py", line 746, in
load_dict
    k = self.marker()
  File "/usr/lib/python2.2/pickle.py", line 600, in
marker
    while stack[k] is not mark: k = k-1
IndexError: list index out of range

[loewis]

Logged In: YES
user_id=21627

The documentation of UnpicklingError says

Note that other exceptions may also be raised during
unpickling, including (but not necessarily limited to)
\exception{AttributeError} and \exception{ImportError}.

So I'm not so sure that there is a bug.

[tchristopher]

Logged In: YES
user_id=64169

Actually, I want EOFError on the file-like object
returning ''; the empty string IS an end of file
indication. That's what I'm looking for when there are a
varying number of objects, and yes, I use it a lot.

So please DO NOT make end of file return an UnpicklingError.

[nascheme]

Logged In: YES
user_id=35752

I added IndexError and EOFError to the list of example
exceptions that unpickle can raise. Closing this bug.