struct unpack issue

[Peter Otten]

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
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
('12', 909456435)

See the second table on http://docs.python.org/lib/module-struct.html for
the options you have.

Peter

 

[Ping Zhao]

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Hi,

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.

Sincerely,

- --
Ping Zhao, PhD Student Dormitory: +82-(0)31-338-9503-0415
Information Engineering (e-mail address removed)
Myongji University http://oceanio.wordpress.com
GMT +09:00 (Seoul)

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