[Python-bugs-list] [ python-Bugs-633152 ] list slice ass ignores subtypes of list

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Wed, 06 Nov 2002 00:45:46 -0800


Bugs item #633152, was opened at 2002-11-04 09:19
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Category: Python Interpreter Core
Group: Python 2.3
Status: Closed
Resolution: Fixed
Priority: 5
Submitted By: Ronald Oussoren (ronaldoussoren)
Assigned to: Nobody/Anonymous (nobody)
Summary: list slice ass ignores subtypes of list

Initial Comment:
When assigning a subtype of list to a list slice the implementation 
of slice-assignment directly accesses the list representation and 
ignores any modified accessor functions:

class MyList  (list):
    def __getitem__(self, idx):
        if idx % 2 == 0:
            return 'E'
        return 'O'

mylst = MyList()
mylst.append(1)
mylst.append(1)

lst = [ 1, 2, 3, 4]
lst [2:3] = mylst
print lst
# prints [1, 2, 1, 1, 4] I'd expect it to print [1, 2, 'E', 'O', 4 ]

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>Comment By: Ronald Oussoren (ronaldoussoren)
Date: 2002-11-06 09:45

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Sorry, but it is not fixed completely. The problem is in PyList_AsTuple 
(called by PySequence_Tuple if the arguments is a PyList). 
PyList_AsTuple directly accesses the list representation, and therefore 
the code above still fails. I'll try to post a patch for this later this week.

I'm not sure why the patch got corrupted, it (and still is) fine on my 
system (but not when I download it again...). 

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Comment By: Michael Hudson (mwh)
Date: 2002-11-05 19:15

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I think this is now fixed, via a somewhat different approach.

You might want to check, though.

While we're at it, there are a bunch of problems with your
patch (for future reference):

1) it contains a bunch of NUL bytes!
2) it's a straight diff.  we like context (-c) or unified
(-u) diffs.  most people prefer context diffs, I think. 
Bass players (e.g. Barry) prefer unified.
3) it has no error checking at all!

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Comment By: Ronald Oussoren (ronaldoussoren)
Date: 2002-11-04 12:04

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The attached patch (list_ass_slice.patch) updates the implementation of 
slice assigment for lists: If the RHS is a list (exact match) use the 
current implementation and if the RHS is a sequence use 
PySequence_GetItem.

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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=633152&group_id=5470