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Newsgroups: comp.lang.python
Date: Tue, 28 Aug 2012 16:55:13 -0700 (PDT)
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Subject: Re: issue with struct.unpack
From: 9bizy <a.m.akingbulu-11@student.lboro.ac.uk>
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On Wednesday, 29 August 2012 00:36:40 UTC+1, MRAB  wrote:
> On 29/08/2012 00:01, 9bizy wrote:> On Tuesday, 28 August 2012 23:49:54 
> 
> UTC+1, MRAB  wrote:
> 
>  >> On 28/08/2012 23:34, 9bizy wrote:
> 
>  >> > This is what I have to reproduce the challenge I am having below:
> 
>  >> >
> 
>  >> > import csv
> 
>  >> > import struct
> 
>  >> >
> 
>  >> > data = []
> 
>  >> >
> 
>  >> > for Node in csv.reader(file('s_data.xls')):
> 
>  >>
> 
>  >> That tries to read the file as CSV, but, judging from the extension,
> 
>  >> it's in Excel's format. You don't even use what is read, i.e. Node.
> 
>  >>
> 
>  >> >      data.append(list((file('s_data.xls'))))
> 
>  >> >
> 
>  >> That opens the file again and 'list' causes it to read the file as
> 
>  >> though it were a series of lines in a text file, which, as I've said,
> 
>  >> it looks like it isn't. The list of 'lines' is appended to the list
> 
>  >> 'data', so that's a list of lists.
> 
>  >> >
> 
>  >> >      data = struct.unpack('!B4HH', data)
> 
>  >> >      print "s_data.csv: ", data
> 
>  >> >
> 
>  >> > I tries so many format for the struct.unpack but I got this errors:
> 
>  >> >
> 
>  >> > Traceback (most recent call last):
> 
>  >> >
> 
>  >> >      data = struct.unpack('!B4HH', data)
> 
>  >> > struct.error: unpack requires a string argument of length 11
> 
>  >> >
> 
>  >> [snip]
> 
>  >> It's complaining because it's expecting a string argument but you're
> 
>  >> giving it a list instead.
> 
>  >
> 
>  > How do I then convert data to a string argument in this case?
> 
>  >
> 
> The question is: what are you trying to do?
> 
> 
> 
> If you're trying to read an Excel file, then you should be trying the
> 
> 'xlrd' module. You can find it here: http://www.python-excel.org/
> 
> 
> 
> If your trying to 'decode' a binary file, then you should open it in
> 
> binary mode (with "rb"), read (some of) it as a byte string and then
> 
> pass it to struct.unpack.

Thank you MRAB this was helpful.