problem with struct module

[Angelo Secchi]

Apparently I solved my problem and this sample (in the Hypothesis that
I have$3$ fields for a total length of 1970) code works:

import struct

fmt='22s16s1932s'

size=struct.calcsize(fmt)

f=file('pan8997.finalevero','rb')

s=f.read(size)

d1,d2,d3=struct.unpack(fmt,line)
 
However I have now a different question that I was not able to solve
looking at the documentation. Suppose I am interested in a field that I
know starts at the 76th position and it is a 3s, How can I get it
directly without make some calculation and write

fmt='75s3s1892s'

Is there a way to say to implement in the format the statement "start
at the 76th position e return a string of length 3" ?

Thanks
a.





but actually I have a different question




On Tue, 24 Feb 2004 16:28:55 +0100
Angelo Secchi <secchi at sssup.it> wrote:

> 
> I'm trying to use the unpack method in the struct module to parse a
> binary file without success. I have a binary file with records that
> include many fields for a total length of 1970. Few days ago I was
> suggested by the list to use the struct module to parse it using the
> following code in the hypothesis that for each records I have just two
> fields:
> 
> import struct
> fmt='10s1960s'
> size=struct.calcsize(fmt)
> f=file("data")
> s=f.read(size)
> 
> while s:
>     print 'read:', s
>     d1,d2=struct.unpack(fmt,s)
>     print 'unpack', d1
> 
> Probably I was not even able to explain my problem since it seem that
> this code is not able to read the file. Can anybody help me, maybe
> asking for other infos they need? Also just suggest me a place where I
> can find examples of using struc.unpack would be very helpful.
> Thanks.
> a.
> 
> 
>