[ python-Bugs-1101399 ] dict subclass breaks cPickle noload()

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Bugs item #1101399, was opened at 2005-01-12 23:37
Message generated for change (Comment added) made by tim_one
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Category: Python Library
Group: None
Status: Open
Resolution: None
Priority: 5
Submitted By: Neil Schemenauer (nascheme)
Assigned to: Jim Fulton (dcjim)
Summary: dict subclass breaks cPickle noload()

Initial Comment:
The attached script displays the bug.

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>Comment By: Tim Peters (tim_one)
Date: 2005-01-13 19:24

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Yup, good catch on append/appends too.  Moral dilemma:  
should undocumented features be tested?  That's a slippery 
slope in cPickle <wink>.

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Comment By: Neil Schemenauer (nascheme)
Date: 2005-01-13 19:06

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New patch.  Checks for invalid marker as suggested by Tim. 
It also  add noload_append() and noload_appends().

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Comment By: Tim Peters (tim_one)
Date: 2005-01-13 13:28

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Oh. fudge.  I'd like to say that since noload() is wholly 
undocumented, tough luck <wink>.

The GLOBAL and NEWOBJ opcodes just stick None on the 
stack in noload()-mode.  That's why the test script yields

TypeError: object does not support item assignment

(SETITEM is griping about the None noload()'s NEWOBJ left 
behind).  I agree your patch fixes that, and offhand can't 
think of a more principled approach.  Assigning to Jim in case 
he can.

In any case, please put the marker() call on a different line 
and check its return value.  I know some other code in 
cPickle takes the shortcut you're using, but it's not a good 
idea to grow more code like that (it changes what would 
have been a clear ""could not find MARK" error into a more 
mysterious "unpickling stack underflow" error).

It would be good to get this fixed in 2.3.5 too.

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Comment By: Neil Schemenauer (nascheme)
Date: 2005-01-12 23:54

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Attached is a patch that seems to fix the problem.  Someone
please review it.

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