[Patches] [ python-Patches-1538606 ] Patch to fix __index__() clipping

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Patches item #1538606, was opened at 2006-08-11 10:51
Message generated for change (Comment added) made by arigo
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Category: Core (C code)
Group: Python 2.5
Status: Open
Resolution: None
Priority: 9
Submitted By: Travis Oliphant (teoliphant)
Assigned to: Neal Norwitz (nnorwitz)
Summary: Patch to fix __index__() clipping

Initial Comment:
This is a patch that builds off of Nick Coghlan's work
to fix the __index__() clipping problem.  

It defines 3 New C-API calls (1 is a macro):

int PyIndex_Check(obj) -- does this object have nb_index

PyObject* PyNumber_Index(obj) -- return nb_index(obj)
if possible

Py_ssize_t PyNumber_AsSsize_t(obj, err) -- return obj
as Py_ssize_t by frist going through nb_index(obj)
which returns an integer or long integer.  If err is
NULL, then clip on Overflow, otherwise raise err on
Overflow encountered when trying to fit the result of
nb_index into a Py_ssize_t slot. 

With these three C-API calls, I was able to fix all the
problems that have been identified and simplify several
pieces of code. 





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>Comment By: Armin Rigo (arigo)
Date: 2006-08-12 10:40

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The check for a negative long needs to be done
differently; this is really depending too much
on internal details.

Note also that the _long_as_ssize_t() function
was introduced to support both long_index() and
_PyLong_AsSsize_t().  Now that the former is
removed, the situation looks slightly strange,
because _long_as_ssize_t() is doing a bit too
much work for its one remaining caller.
That's why somehow reusing _long_as_ssize_t()
from abstract.c would look cleaner to me.

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Comment By: Travis Oliphant (teoliphant)
Date: 2006-08-11 19:16

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I've made the changes Armin suggested.  I changed
operator.index to go back to its original behavior of
returning a.__index__()

I'm +0 on adding _PyLong_AsClippedSsize_t to clean-up the
check for a negative long integer. 

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Comment By: Armin Rigo (arigo)
Date: 2006-08-11 17:15

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I like this API too, and the patch looks good
apart from some more details:

A style note first: some lines are indented with 
spaces instead of tabs.  This causes some
changes on otherwise-unchanged lines, too.

if PyIndex_Check(key)   =>   if (PyIndex_Check(key))

typeobject.c: slot_nb_index() may not need to do 
the type-checking because it is done anyway in 
the caller, which can only be PyNumber_Index().

classobject.c: same remark about instance_index().

unicodeobject.c: kill macro HAS_INDEX
mmapmodule.c:    idem
arraymodule.c:   idem

should operator.index(o) return 
PyNumber_AsSsize_t(o) or just PyNumber_Index(o)? 
I can think of use cases for the latter, which
is somehow the most primitive of the two, so it
should IMHO be exposed via the operator module.

docs: "possitive" => "positive"


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Comment By: Nick Coghlan (ncoghlan)
Date: 2006-08-11 11:47

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The PyNumber_Index docs should explicitly state that it
raises IndexError when overflow occurs.

It may also be worth resurrecting _PyLong_AsClippedSsize_t
in order to clean up the implementation of
PyNumber_AsSsize_t (detecting OverflowError then poking
around in the guts of a long object is a bit ugly).

Other than that, looks good to me (I like this API a lot
better than mine).

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