issue with struct.unpack

Tue Aug 28 19:55:13 EDT 2012

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.