struct unpack newline

[grant at idscape.co.za]

Hi ,

Thanks for the tip regarding checking the length of line. I discovered
that on the problem record it was short by a few bytes. After changing
the read method from "for line in.." to "infile.read(n)" my problem was
solved,
what concerns me though is that although the file is opened in binary
mode,
"for line.." has a problem reading the file correctly.

Thanks
Grant


Fredrik Lundh wrote:
> grant at idscape.co.za wrote:
>
> > I am pretty new to python and am having a problem
> > intepreting binary data using struct.unpack.
> > I am reading a file containing binary packed data
> > using open with "rb". All the values are coming through
> > fine when using (integer1,) = struct.unpack('l', line[86:90])
> > except when line[86:90] contains "carriage-return" "linefeed"
> > which are valid binary packed values. Error = unpack
> > string size dows not match format. It seems that
> > struct, instead of reading 4 bytes for line[86:90]
> > only reads 2 bytes if the second byte is CR or LF.
>
> verifying that struct doesn't care about newlines is of course
> pretty trivial:
>
> >>> import struct
> >>> struct.unpack("l", "\0\0\0\0")
> (0,)
> >>> struct.unpack("l", "\0\r\0\0")
> (3328,)
> >>> struct.unpack("l", "\0\n\0\0")
> (2560,)
>
> have you verified that len(line) really is what you think?
>
> >>> struct.unpack("l", "\0\r\n\0")
> (658688,)
> >>> struct.unpack("l", "\0\n\0")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> struct.error: unpack str size does not match format
> 
> </F>