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I'm messing around with making a binary data parser, and while I could fall back on C, I wanted to see if I could use Python for the task. I have some inkling of how to get this going, and my current implementation looks something like this: from ctypes import * class sHeader(Structure): _fields_ = [("CC", c_uint8, 4), ("AFC", c_uint8, 2), ("TSC", c_uint8, 2), ("PID", c_uint16, 13), ("TP", c_uint16, 1), ("PSI", c_uint16, 1), ("TEI", c_uint16, 1), ("SyncByte", c_uint8)] class Header(Union): _fields_ = [("sData", sTsHeader), ("ulData", c_uint32)] head = Header() head.ulData = 0xffffffff print(head.ulData) print(head.sData.SyncByte) print(sHeader.SyncByte) print(sHeader.TEI) print(sHeader.PSI) print(sHeader.TP) print(sHeader.PID) print(sHeader.TSC) print(sHeader.AFC) print(sHeader.CC) print(sizeof(sHeader)) print(sizeof(c_uint8)) print(sizeof(c_uint16)) print(sizeof(c_uint32)) Which produces this output: V:\>C:\Python27\python.exe WidiUnpacker.py 0xffffffffL 0x0 <Field type=c_ubyte, ofs=4, size=1> <Field type=c_ushort, ofs=2:15, bits=1> <Field type=c_ushort, ofs=2:14, bits=1> <Field type=c_ushort, ofs=2:13, bits=1> <Field type=c_ushort, ofs=2:0, bits=13> <Field type=c_ubyte, ofs=0:6, bits=2> <Field type=c_ubyte, ofs=0:4, bits=2> <Field type=c_ubyte, ofs=0:0, bits=4> 6 1 2 4 So... Looks to me like my bytes aren't bytes so much as words. I don't know enough about Python or ctypes to understand why that is, but it's kind of defeating my purpose at the moment. Any ideas?

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