open for append ('a')

[Bong]

I can successfully open a file for reading ('r') or writing ('w') but I'm trying to open for updating ('a') and I can't get it to work.

I set a variable, outfile to 'x:/projmn/time.txt'. This file (and path) exists.
I then do:

try: f = open(outfile,'a')
except:
        a=raw_input("could not open "+outfile+" (press Enter).")
        exit()

and I get the error. I've also tried 'a+', and 'r+' with the same problem. I'm running on Windows XP with Python 2.4. Is there something I'm doing wrong?

_________________
Bob Rashkin

 

[mikrom]

> ..and I get the error
Which error ? Post it and we will see.

 

[mikrom]

Your example works with me without problem. For example I have this file named myfile.txt

line 1
line 2

and the following code

outfile="myfile.txt"
try: 
  f = open(outfile,'r+')
except:
  a=raw_input("could not open "+outfile+" (press Enter).")
  exit()
# now reading  
lines=f.readlines()
for line in lines:
  print line
# now appending
f.write("\nNow appending this at end")
f.close()

After running the script, it first prints the 2 lines and then appends the 3rd line, so the resulting myfile.txt is:

line 1
line 2
Now appending this at end

If you try to open the file with

f = open(outfile,'a')

then you cannot read the file, you can only append somthing at the end of file. If you try to read the file, you get an error:

Traceback (most recent call last):
  File "C:\Users\Roman\Work\pok2.py", line 8, in <module>
    lines=f.readlines()
IOError: [Errno 9] Bad file descriptor

So you need to comment-out the reading and then appending works:

outfile="myfile.txt"
try: 
  f = open(outfile,'a')
except:
  a=raw_input("could not open "+outfile+" (press Enter).")
  exit()
# now reading  
#lines=f.readlines()
#for line in lines:
#  print line
# now appending
f.write("\nNow appending this at end")
f.close()

 

[Bong]

It's actually rather strange. The error I get is

I/O error(2): No such file or directory
could not open x:/projMn/time.txt

However, when I execute the exact same statement (f=open('x:/projMn/time.txt','a')) interactively from a shell, I get no error.

_________________
Bob Rashkin

 

[Bong]

OK.
Problem solved. I was reading the filename in incorrectly.
Thanks for the help.

_________________
Bob Rashkin

 

[mikrom]

I can't believe it, how it is possible. If you have treated the exception as showed above i.e

outfile='x:/projMn/time.txt'
try: 
  f = open(outfile,'a')
except:
  a=raw_input("could not open "+outfile+" (press Enter).")
  exit()

and the path 'x:/projMn/time.txt' not exists, you should get this message

could not open x:/projMn/time.txt (press Enter).

If the path exists and the file don't exists, then the file will be created.

Try to change the path to file
from

outfile='x:/projMn/time.txt'

to this form

outfile='x:\\projMn\\time.txt'

 

[Bong]

As I said, I was reading in the file name incorrectly. I didn't realize that the appended '\n' was there and needed to be stripped. Doing so fixed everything.

_________________
Bob Rashkin