Bob
At 19:52 03/02/2009, you wrote:
etrade.griffi...@dsl.pipex.com wrote:
Data format:
TIME 1 F 0.0
DISTANCE 10 F 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0
F=float, D=double, L=logical, S=string etc
The first part of the file should contain a string (eg "TIME"),
an integer (1) and another string (eg "F") so I tried using
import struct
in_file = open(file_name+".dat","rb")
data = in_file.read()
items = struct.unpack('sds', data)
Now I get the error
error: unpack requires a string argument of length 17
which has left me completely baffled!
Did you open the file with mode 'b'? If not change that.
You are passing the entire file to unpack when you should be giving
it only the first "line". That's why is is complaining about the
length. We need to figure out the lengths of the lines.
Consider the first "line"
TIME 1 F 0.0
There were (I assume) 4 FORTRAN variables written here: character
integer character float. Without knowing the lengths of the
character variables we are at a loss as to what the struct format
should be. Do you know their lengths? Is the last float or double?
Try this: print data[:40] You should see something like:
TIME...\x01\x00\x00\x00...F...\x00\x00\x00\x00...DISTANCE...\n\x00\x00\x00
where ... means 0 or more intervening stuff. It might be that the
\x01 and the \n are in other places, as we also have to deal with
"byte order" issues.
Please do this and report back your results. And also the FORTRAN
variable types if you have access to them.
Apologies if this is getting a bit messy but the files are at a
remote location and I forgot to bring copies home. I don't have
access to the original FORTRAN program so I tried to emulate the
reading the data using the Python script below. AFAIK the FORTRAN
format line for the header is (1X, 1X, A8, 1X, 1X, I6, 1X, 1X,
A1). If the data following is a float it is written using n(1X,
F6.2) where n is the number of records picked up from the preceding header.
# test program to read binary data
import struct
# create dummy data
data = []
for i in range(0,10):
data.append(float(i))
# write data to binary file
b_file = open("test.bin","wb")
b_file.write(" %8s %6d %1s\n" % ("DISTANCE", len(data), "F"))
for x in data:
b_file.write(" %6.2f" % x)
b_file.close()
# read back data from file
c_file = open("test.bin","rb")
data = c_file.read()
start, stop = 0, struct.calcsize("2s8s2si2s1s")
items = struct.unpack("2s8s2si2s1s",data[start:stop])
print items
print data[:40]
I'm pretty sure that when I tried this at the other PC there were a
bunch of \x00\x00 characters in the file but they don't appear in
NotePad ... anyway, I thought the Python above would unpack the data
but items appears as
(' ', 'DISTANCE', ' ', 538976288, '10', ' ')
which seems to be contain an extra item (538976288)
Alun Griffiths
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