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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