etrade.griffi...@dsl.pipex.com wrote:
Hi
following last week's discussion with Bob Gailer about reading unformatted FORTRAN files, I have attached an example of the file in ASCII format and the equivalent unformatted version.
Thank you. It is good to have real data to work with.
Below is some code that works OK until it gets to a data item that has no additional associated data, then seems to have got 4 bytes ahead of itself.
Thank you. It is good to have real code to work with.
I though I had trapped this but it appears not. I think the issue is asociated with
"newline" characters or the unformatted equivalent.
I think not, But we will see.
I fail to see where the problem is. The data printed below seems to
agree with the files you sent. What am I missing?
FWIW a few observations re coding style and techniques.
1) put the formats in a dictionary before the while loop:
formats = {'INTE': '>i', 'CHAR': '>8s', 'LOGI': '>i', 'REAL': '>f',
'DOUB': '>d', 'MESS': ''>d,}
2) retrieve the format in the while loop from the dictionary:
format = formats[vals[3]]
3) condense the 3 infile lines:
data = open("test.bin","rb").read()
4) nrec is a misleading name (to me it means # of records), nbytes would
be better.
5) Be consistent with the format between calcsize and unpack:
struct.calcsize('>4s8si4s8s')
6) Use meaningful variable names instead of val for the unpacked data:
blank, name, length, typ = struct.unpack ... etc
7) The format for MESS should be '>d' rather than '>%dd' % nval. When
nval is 0 the for loop will make 0 cycles.
8) You don't have a format for DATA (BEGI); therefore the prior format
(for CHAR) is being applied. The formats are the same so it does not
matter but could be confusing later.
# Test function to write/read from unformatted files
import sys
import struct
# Read file in one go
in_file = open("test.bin","rb")
data = in_file.read()
in_file.close()
# Initialise
nrec = len(data)
stop = 0
items = []
# Read data until EOF encountered
while stop < nrec:
# extract data structure
start, stop = stop, stop + struct.calcsize('4s8si4s8s')
vals = struct.unpack('>4s8si4s8s', data[start:stop])
items.extend(vals)
print stop, vals
# define format of subsequent data
nval = int(vals[2])
if vals[3] == 'INTE':
fmt_string = '>i'
elif vals[3] == 'CHAR':
fmt_string = '>8s'
elif vals[3] == 'LOGI':
fmt_string = '>i'
elif vals[3] == 'REAL':
fmt_string = '>f'
elif vals[3] == 'DOUB':
fmt_string = '>d'
elif vals[3] == 'MESS':
fmt_string = '>%dd' % nval
else:
print "Unknown data type ... exiting"
print items
sys.exit(0)
# extract data
for i in range(0,nval):
start, stop = stop, stop + struct.calcsize(fmt_string)
vals = struct.unpack(fmt_string, data[start:stop])
items.extend(vals)
# trailing spaces
if nval > 0:
start, stop = stop, stop + struct.calcsize('4s')
vals = struct.unpack('4s', data[start:stop])
# All data read so print items
print items
-------------------------------------------------
Visit Pipex Business: The homepage for UK Small Businesses
Go to http://www.pipex.co.uk/business-services
------------------------------------------------------------------------
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
--
Bob Gailer
Chapel Hill NC
919-636-4239
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
