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>>> a=20
>>> b=400
>>> str=struct.pack('ii',a,b)
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>>> print len(str)
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8
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>>> print repr(str)
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#ÆäÖÐÊ®Áù½øÖÆµÄ 0x00000014, 0x00000190·Ö±ð±íʾ20ºÍ400
>>>
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format = "!HH%ds" % len(data)
buffer = struct.pack(format,opcode,blocknumber,data)
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struct.unpack():
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>>> a1,a2=struct.unpack('ii',str)
>>> print 'a1',a1
a1 20
>>> print 'a2=',a2
a2= 400
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>>> struct.calcsize('HH4s')
8
>>> struct.calcsize('ii')
8
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