[Python-bugs-list] [ python-Bugs-504723 ] Bad exceptions from pickle

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Bugs item #504723, was opened at 2002-01-17 03:55
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Category: Python Library
Group: Python 2.2
>Status: Closed
>Resolution: Invalid
Priority: 5
Submitted By: Bob Alexander (bobalex)
Assigned to: Nobody/Anonymous (nobody)
Summary: Bad exceptions from pickle

Initial Comment:
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


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>Comment By: Neil Schemenauer (nascheme)
Date: 2002-03-22 22:18

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

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Comment By: Thomas W. Christopger (tchristopher)
Date: 2002-02-26 15:59

Message:
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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.

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Comment By: Martin v. Löwis (loewis)
Date: 2002-01-17 07:41

Message:
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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.

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