issue with struct.unpack
I am trying to unpack values from sensor data I am retrieving through a serial
cable, but I get errors while using struct.unpack, how can I use struct.unpack
to unload the data in a readable format?
I checked the python documentation for struct and I can seen to find any
argument for this.
I have data = struct.unpack('char',data) but I still get errors
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Re: issue with struct.unpack
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')):
data.append(list((file('s_data.xls'
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
On Saturday, 25 August 2012 19:34:39 UTC+1, 9bizy wrote:
> I am trying to unpack values from sensor data I am retrieving through a
> serial cable, but I get errors while using struct.unpack, how can I use
> struct.unpack to unload the data in a readable format?
>
>
>
> I checked the python documentation for struct and I can seen to find any
> argument for this.
>
>
>
> I have data = struct.unpack('char',data) but I still get errors
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Re: issue with struct.unpack
On Saturday, 25 August 2012 20:16:54 UTC+1, MRAB wrote:
> On 25/08/2012 19:34, 9bizy wrote:
>
> > I am trying to unpack values from sensor data I am retrieving through
>
> > a serial cable, but I get errors while using struct.unpack, how can I
>
> > use struct.unpack to unload the data in a readable format?
>
> >
>
> > I checked the python documentation for struct and I can seen to find
>
> > any argument for this.
>
> >
>
> > I have data = struct.unpack('char',data) but I still get errors
>
> >
>
> The format strings are described here for Python 3:
>
>
>
> http://docs.python.org/3.2/library/struct.html
>
>
>
> and here for Python 2:
>
>
>
> http://docs.python.org/2.7/library/struct.html
I used this documents but they do not explain or provide an example on how to
use struct.unpack for sensor data from an external source or even data from a
excel sheet.
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Re: issue with struct.unpack
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?
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Re: issue with struct.unpack
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.
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