Ping Zhao wrote:
> I am writing a small program to decode MS bitmap image. When I use
> statements as follow, it works fine:
>
> header['sig'] = str(struct.unpack('2s', self.__read(src, 2))[0])
> header['len'] = int(struct.unpack('1i', self.__read(src, 4))[0])
>
> However, when I tried to rewrite them in short:
>
> header = struct.unpack('2s1i', self.__read(src, 6))
>
> The Python interpreter in my Linux box came up with an error:
>
> ...
> header = struct.unpack('2s1i', self.__read(src, 6))
> File "/usr/lib/python2.5/struct.py", line 87, in unpack
> return o.unpack(s)
> struct.error: unpack requires a string argument of length 8
>
> It was weired that the required argument length increased to 8. Any idea
> on this? I am using a 32bit pentium-m and the picture file was stored in
> little-edian format.
Try specifying byte order and alignment:
>>> struct.unpack("2s1i", "123456")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/lib/python2.5/struct.py", line 87, in unpack
return o.unpack(s)
struct.error: unpack requires a string argument of length 8
>>> struct.unpack("=2s1i", "123456")
('12', 909456435)
See the second table on http://docs.python.org/lib/module-struct.html for
the options you have.
Peter
--
http://mail.python.org/mailman/listinfo/python-list
