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POPython structure always stuck at 0 no matter what value you assign to it?
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2010-09-29T18:17:31.207
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I was writing a module to compact bits to be passed to C program, but keep getting errors. After some tests, I found out that the field a of class Blah is stuck at 0 no matter what. Does anyone know if this is a bug or if I'm doing something wrong here? Sorry, I forgot to mention I'm using python 3.1.2 from <a href="http://www.python.org/download/releases/3.1.2/" rel="nofollow">http://www.python.org/download/releases/3.1.2/</a> <pre><code>>>> import ctypes >>> class Blah(ctypes.Structure): ... _fields_ = [("a", ctypes.c_uint64, 64), ... ("b", ctypes.c_uint16, 16), ... ("c", ctypes.c_uint8, 8), ... ("d", ctypes.c_uint8, 8)] ... >>> x = Blah(0xDEAD,0xBEEF,0x44,0x12) >>> print (hex(x.a) ) 0x0 >>> print (hex(x.b )) 0xbeef >>> print (hex(x.c )) 0x44 >>> print (hex(x.d )) 0x12 >>> >>> g = Blah(0x2BAD,0xBEEF,0x55,0x12) >>> print (hex(g.a )) 0x0 >>> print (hex(g.b )) 0xbeef >>> print (hex(g.c )) 0x55 >>> print (hex(g.d )) 0x12 >>> </code></pre> swapping first two fields' position gives same result <pre><code>>>> import ctypes >>> class Blah(ctypes.Structure): ... _fields_ = [("a", ctypes.c_uint16, 16), ... ("b", ctypes.c_uint64, 64), ... ("c", ctypes.c_uint8, 8), ... ("d", ctypes.c_uint8, 8)] ... >>> x = Blah(0xDEAD,0xBEEF,0x44,0x12) >>> print (hex(x.a) ) 0xdead >>> print (hex(x.b )) 0x0 >>> print (hex(x.c )) 0x44 >>> print (hex(x.d )) 0x12 >>> >>> g = Blah(0x2BAD,0xBEEF,0x55,0x12) >>> print (hex(g.a )) 0x2bad >>> print (hex(g.b )) 0x0 >>> print (hex(g.c )) 0x55 >>> print (hex(g.d )) 0x12 >>> </code></pre> varying field's size and I observe some weird cutoff of the input <pre><code>>>> import ctypes >>> class Blah(ctypes.Structure): ... _fields_ = [("a", ctypes.c_uint64, 40), ... ("b", ctypes.c_uint64, 40), ... ("c", ctypes.c_uint8, 8), ... ("d", ctypes.c_uint8, 8)] ... >>> x = Blah(0xDEAD,0xBEEF,0x44,0x12) >>> print (hex(x.a) ) 0xad >>> print (hex(x.b )) 0xef >>> print (hex(x.c )) 0x44 >>> print (hex(x.d )) 0x12 >>> >>> g = Blah(0x2BAD,0xBEEF,0x55,0x12) >>> print (hex(g.a )) 0xad >>> print (hex(g.b )) 0xef >>> print (hex(g.c )) 0x55 >>> print (hex(g.d )) 0x12 >>> </code></pre> Does anyone know why is this happening?
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<python><structure>
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Python structure always stuck at 0 no matter what value you assign to it?
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1. COLooks like a bug to me. I've opened a bug report: http://bugs.python.org/issue9989
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 POPython structure always stuck at 0 no matter what value you assign to it?
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2. COthanks, I guess it's a serious bug then. this makes the Structure module unreliable in Python 3.1.2 on WindowsXP SP3 x86
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