[issue12974] array module: deprecate '__int__' conversion support for array elements

[Serhiy Storchaka]

Change by Serhiy Storchaka :


--
resolution:  -> duplicate
stage: needs patch -> resolved
status: open -> closed
superseder:  -> Deprecate implicit truncating when convert Python numbers to C 
integers: use __index__, not __int__

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

See more general issue36048.

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Oren Milman]

Changes by Oren Milman :


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nosy: +Oren Milman

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Serhiy Storchaka]

Changes by Serhiy Storchaka :


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nosy: +serhiy.storchaka

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Stefan Krah]

Changes by Stefan Krah stefan-use...@bytereef.org:


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nosy:  -skrah

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

I just discovered that struct packs pointers from objects with an
__index__() method. Is that intentional?

 import struct
 class IDX(object):
... def __init__(self, value):
... self.value = value
... def __index__(self):
...  return self.value
... 
 struct.pack('P', IDX(9))
b'\t\x00\x00\x00\x00\x00\x00\x00'


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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Mark Dickinson]

Mark Dickinson dicki...@gmail.com added the comment:

Yes, that's intentional.  When use of __int__ was deprecated, a bug report 
popped up from someone who wanted to be able to have their own objects treated 
as integers for the purposes of struct.pack.  (I don't recall which issue;  
Meador, do you remember?)  So we added use of __index__ at that point.

I think __index__ is the right interface for something to expose if it wants to 
be usable as an integer, and this usage is consistent with the original 
__index__ PEP.

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

Mark Dickinson rep...@bugs.python.org wrote:
 Yes, that's intentional.  When use of __int__ was deprecated, a bug
 report popped up from someone who wanted to be able to have their own
 objects treated as integers for the purposes of struct.pack. 
 (I don't recall which issue;  Meador, do you remember?)
  So we added use of __index__ at that point.

Yes, I think that's #1530559, and the bug report was about PyCUDA. I can
see why 'bBhHiIlLqQ' allow __index__(), since they previously allowed
__int__().

I specifically meant the 'P' format. As far as I can see, PyLong_AsVoidPtr()
never allowed __int__(), but now index objects can be packed as pointers.
It isn't a big deal, I just have to know for features/pep-3118.

To illustrate, this is python2.5.0; INT is an object with an __int__() method:

'\x07\x00\x00\x00\x00\x00\x00\x00'
 struct.pack('P', INT(7))
Traceback (most recent call last):
  File stdin, line 1, in module
  File /home/stefan/hg/r25/Lib/struct.py, line 63, in pack
return o.pack(*args)
struct.error: cannot convert argument to long


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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Meador Inge]

Meador Inge mead...@gmail.com added the comment:

 I specifically meant the 'P' format. As far as I can see, PyLong_AsVoidPtr()
 never allowed __int__(), but now index objects can be packed as pointers.
 It isn't a big deal, I just have to know for features/pep-3118.

 To illustrate, this is python2.5.0; INT is an object with an __int__() method:

 '\x07\x00\x00\x00\x00\x00\x00\x00'
 struct.pack('P', INT(7))
 Traceback (most recent call last):
  File stdin, line 1, in module
  File /home/stefan/hg/r25/Lib/struct.py, line 63, in pack
    return o.pack(*args)
 struct.error: cannot convert argument to long

Huh, that's interesting.  It doesn't allow 'unsigned long' packs either (2.6.7):

Python 2.6.7+ (unknown, Sep 16 2011, 09:53:25)
[GCC 4.6.0 20110603 (Red Hat 4.6.0-10)] on linux2
Type help, copyright, credits or license for more information.
 import struct
 class IDX(object):
... def __init__(self, value):
... self.value = value
... def __int__(self):
...  return self.value
...
 for code in ['l', 'L', 'P']:
...try:
...   struct.pack(code, IDX(9))
...except Exception as e:
...   print pack('%s'): %s % (code, e)
...
'\t\x00\x00\x00'
pack('L'): unsupported operand type(s) for : 'IDX' and 'long'
pack('P'): cannot convert argument to long

The behavior around '__int__' in previous versions seems somewhat accidental.

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Stefan Krah]

Stefan Krah stefan-use...@bytereef.org added the comment:

Meador Inge rep...@bugs.python.org wrote:
 The behavior around '__int__' in previous versions seems somewhat accidental.

I think struct followed the functions in longobject.c, which is not
really consistent with respect to duck typing. See also #12965 or
http://bugs.python.org/issue1172711#msg48086.

But I think that the decision to accept __index__() for both signed
and unsigned integer formats is good for consistency.

For 'P' I'm not sure, but course it might be used in the wild by now.

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[issue12974] array module: deprecate '__int__' conversion support for array elements

[Meador Inge]

New submission from Meador Inge mead...@gmail.com:

When reviewing the fix for issue1172711 it was discovered that the 'array' 
module allows for '__int__' conversions:

 import array, struct
 a = array.array('L', [1,2,3])
 class T(object):
... def __init__(self, value):
... self.value = value
... def __int__(self):
...  return self.value
...
 a = array.array('L', [1,2,3])
 struct.pack_into('L', a, 0, 9)
 a
array('L', [9, 2, 3])
 a[0] = T(100)
 a
array('L', [100, 2, 3])

As discussed in issue1172711, this behavior may not be desirable.  We should 
look at deprecating '__int__' and adding '__index__' as was done for the struct 
module in issue1530559.

--
components: Library (Lib)
messages: 144000
nosy: mark.dickinson, meadori, skrah
priority: normal
severity: normal
stage: needs patch
status: open
title: array module: deprecate '__int__' conversion support for array elements
type: behavior
versions: Python 3.3

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