Python ctypes 模块，LittleEndianStructure() 实例源码

def check_ctypes_datatype(datatype):
    valid_datatypes = (
        ctypes._SimpleCData,
        ctypes.Union,
        ctypes.BigEndianStructure,
        ctypes.LittleEndianStructure,
        ctypes.Structure,
        )
    for t in valid_datatypes:
        if issubclass(datatype, t):
            return
    raise TypeError('datatype must be a ctypes data type, but was {}'.format(datatype.__name__))

def read_mbr(image):
    """Read an MBR with ctypes and return it.  Not for general use.  Works
    with the MBRs in the Raspbian images we test, not tested with anything
    else.  Mostly used as a fun second opinion to parted which is used in
    the tool under testing.
    """
    class Partition(LittleEndianStructure):
        """https://en.wikipedia.org/wiki/Master_boot_record#Partition_table_entries"""
        SECTOR_SIZE = 512
        _pack_ = 1
        _fields_ = [("status",    c_ubyte),
                    ("chs_begin", c_ubyte * 3),
                    ("type",      c_ubyte),
                    ("chs_end",   c_ubyte * 3),
                    ("lba_begin", c_uint),
                    ("lba_size",  c_uint),
                   ]

        @property
        def begin(self):
            """Convenience function for returning begin in bytes."""
            return self.lba_begin * self.SECTOR_SIZE

        @property
        def size(self):
            """Convenience function for returning size in bytes."""
            return self.lba_size * self.SECTOR_SIZE
    assert sizeof(Partition) == 16, "Partition definition error"

    class MBR(LittleEndianStructure):
        """https://en.wikipedia.org/wiki/Master_boot_record#Sector_layout"""
        _pack_ = 1
        _fields_ = [("skip",       c_ubyte * 446),
                    ("partitions", Partition * 4),
                    ("signature",  c_ubyte * 2),
                   ]
    assert sizeof(MBR) == 512, "MBR definition error"

    with open(image, "rb") as img:
        mbr = MBR.from_buffer(bytearray(img.read(sizeof(MBR))))
        assert bytes(mbr.signature) == b"\x55\xAA", "Invalid MBR signature."
        return mbr