'Return decoded data from file.
@param fmt: See U{struct<http://docs.python.org/lib/module-struct.html>}
@param start: Position in file from which to decode'

@safe
def unpack(self, fmt=DWORD, start=0):

    end = (start + struct.calcsize(fmt))
    self._file.seek(start)
    ret = struct.unpack(fmt, self._file.read((end - start)))
    return ret
