Hello,
Maybe this will do the trick:
>>> print '0x%x' % (-2 & int('ffffffff',16))
0xfffffffe
As you can see, it works for negative numbers (-2).
Also, I used int('ffffffff',16) instead of 0xffffffffL, since you
indicated that won't work in Python 3.0. I don't know if this
alternative will work (I don't have Python 3.0).
Dennis
D.Hendriks (Dennis) wrote:
>Hello,
>
> > val = struct.unpack("I", struct.pack("i", id(self)))
>
>This may not always work. The struct module (according to
>http://docs.python.org/library/struct.html) can be used to
>"[perform] conversions between Python values and C structs
>represented as Python strings". The struct.pack("i", id(self)) call
>converts the result from id(self) to a C struct. The "i" means that
>the C struct will contain a C 'int'. The unpack call will convert
>the C 'int' variable back into a Python value by interpreting the
>C 'int' as an 'unsigned int'. This is why the result of printing is
>a non-negative value when packing/unpacking.
>
>According to the Python documentation at
>http://docs.python.org/library/functions.html, the id(...)
>function may return an integer or long integer. Packing
>a long integer with "i" is problematic:
>
> >>> import sys
> >>> import struct
> >>> struct.pack('i', sys.maxint)
>'\xff\xff\xff\x7f'
> >>> struct.pack('i', sys.maxint+1)
>Traceback (most recent call last):
> File "<stdin>", line 1, in ?
>OverflowError: long int too large to convert to int
>
>This may not be the only issue. According to the documentation of
>struct: "By default, C numbers are represented in the machine’s
>native format and byte order, and properly aligned by skipping
>pad bytes if necessary (according to the rules used by the C
>compiler)." Therefore it may not give consistent results on different
>machines? You could supply specific byte order, size and alignment
>options (standard instead of native), thereby solving that
>problem?
>
>I'm not sure about all the details of the above. Some of it may
>be incorrect. However, if you decide to use it, you better first
>make sure it ALWAYS works.
>
>Dennis
>
>
>
>A.T.Hofkamp wrote:
>
>
>
>>David Beazley wrote:
>>
>>
>>
>>>I can't replicate any of the warning messages you report--even with
>>>Python 2.3
>>>Are you running Python in some special mode or with special command
>>>line options?
>>>
>>>
>>The problem appears when the highest bit of the int is set (bit 31 of
>>a 32 bit number).
>>
>>In Python 2.4 (and higher, apparently), such a value is considered to
>>be negative, while older Pythons consider such values to be unsigned
>>with %u, %o, %x, and %X string formatting.
>>
>>Problem and fix in the program below (although I do not understand how
>>the fix works):
>>
>>================================================
>># prn_id.py
>>import struct
>>
>>class A(object):
>> def p(self): # Demonstrates the problem
>> print "p:id(self)=0x%x" % id(self)
>>
>> def q(self): # Casting does not work (other than removing the
>>warning)
>> print "q:id(self)=0x%x" % long(id(self))
>>
>> def y(self): # This fixes the problem
>> val = struct.unpack("I", struct.pack("i", id(self)))
>> print "y:id(self)=0x%x" % val
>>
>>a = A()
>>print "---------"
>>print "P:"
>>a.p()
>>print "---------"
>>print "Q:"
>>a.q()
>>print "---------"
>>print "Y:"
>>a.y()
>>print "---------"
>>================================================
>>
>>$ python2.3 prn_id.py
>>---------
>>P:
>>prn_id.py:5: FutureWarning: %u/%o/%x/%X of negative int will return a
>>signed string in Python 2.4 and up
>> print "p:id(self)=0x%x" % id(self)
>>p:id(self)=0xb7ef8fac
>>---------
>>Q:
>>q:id(self)=0x-48107054
>>---------
>>Y:
>>y:id(self)=0xb7ef8fac
>>---------
>>
>>Notice the negative value printed by a.q()
>>
>>================================================
>>
>>$ python2.4 prn_id.py
>>---------
>>P:
>>p:id(self)=0x-480fc9f4
>>---------
>>Q:
>>q:id(self)=0x-480fc9f4
>>---------
>>Y:
>>y:id(self)=0xb7f0360c
>>---------
>>
>>Python 2.4 prints a negative value more often (as promised by the
>>FutureWarning).
>>
>>================================================
>>
>>Sincerely,
>>Albert
>>
>>
>>
>
>
>>
>
>
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