[Tutor] open(file, 'rw') problem

[Dave S]

Good morning,

I am having a problem with file open, read & write. The example shows my 
problem. I would have expected it to print a sequence 1,2,3,4 incrementing 
every time it is run. 

#!/usr/bin/env python
import os, shutil, time

basher_dir = '/home/dave/PodCasts'

bit_bucket = basher_dir + '/xbit_bucket'
cd_count = bit_bucket + '/xcd_count'

if not os.path.isfile(cd_count):
	f = open(cd_count, 'w')
	f.write('0')
	f.close()
	
f = open(cd_count,'rw')
n = int(f.read())
n += 1

print n
f.seek(0)
f.write(str(n))
f.close()

Instead I get ...

dave at dave-comp:~/my_files/python_develop/unison/podsplit$ ./test.py
1
Traceback (most recent call last):
  File "./test.py", line 20, in ?
    f.write(str(n))
IOError: [Errno 9] Bad file descriptor
dave at dave-comp:~/my_files/python_develop/unison/podsplit$

It appears to be a problem with me opening the file as 'rw' although I have 
googled and opening as 'rw' appears legal. Can you only open a file as 'r' 
or 'w' -  ie open & close the file twice ?

Any ideas

Cheers

Dave