ftplib in combination with os.unlink in python

Question

With the following code I upload file.txt to a ftp server. When the file has been uploaded I delete it on my local machine.

import os
from ftplib import FTP

HOST = 'host.com'
FTP_NAME = 'username'
FTP_PASS = 'password'
filepath = 'C:\file.txt'
while True:
    try:
        ftp = FTP(HOST)
        ftp.login(FTP_NAME, FTP_PASS)
        file = open(filepath, 'r')
        ftp.storlines('STOR file.txt', file)
        ftp.quit()
        file.close() # from this point on the file should not be in use anymore
        print 'File uploaded, now deleting...'
    except all_errors as e: #EDIT: Got exception here 'timed out'
        print 'error'       #      then the upload restarted.
        print str(e)

os.unlink(filepath) # now delete the file

The code works, but sometimes (every ~10th upload) I get this error message:

Traceback (most recent call last):
in os.unlink(filepath)
WindowsError: [Error 32] The process cannot access the file
because it is being usedby another process: 'C:\file.txt'

So the file cannot be deleted because 'it has not been released' or something? I also tried to unlink the file this way:

while True: # try to delete the file until it is deleted...
    try:
        os.unlink(filepath)
        break
    except all_errors as e:
        print 'Cannot delete the File. Will try it again...'
        print str(e)

But with the "try except block" I also get the same error "The process cannot access the file because it is being usedby another process"! The script didn't even try to print the exception:

'Cannot delete the File. Will try it again...'

and just stopped (like above).

How can I make os.unlink do his job properly? Thanks!

Answer 1

import os
from ftplib import FTP

HOST = 'host.com'
FTP_NAME = 'username'
FTP_PASS = 'password'
filepath = 'C:\file.txt'
file = open(filepath, 'r')
while True:
    try:
        ftp = FTP(HOST)
        ftp.login(FTP_NAME, FTP_PASS)        
        ftp.storlines('STOR file.txt', file)
    except all_errors as e: #EDIT: Got exception here 'timed out'
        print 'error'       #      then the upload restarted.
        print str(e)
    else:
        ftp.quit()
        file.close() # from this point on the file should not be in use anymore
        print 'File uploaded, now deleting...'   
        os.unlink(filepath) # now delete the file
        break

Answer 2

You need to close (file and ftp session) on the except leg of the try/except, else the file keeps being referenced by the "old" timed-out ftp session (so as a consequence you need to open the file within the while loop, not outside it) -- it's not enough to close the file and ftp session on the else leg as that doesn't get rid of the references from the failed, timed out attempts (if any).

Answer 3

I have still problems with the code, it is not as robust as I need it to be. For example it is possible that the login process fails. Maybe user+pass is wrong, maybe the sesrver is busy.

try:
    ftp = FTP(HOST) # HOST is a valid host address
    ftp.login('test', 'test111111') # WRONG user + pass to test code robustness
    ftp.quit()
except all_errors as e:
    ftp.quit()
    print str(e)

The problem is the ftp.quit() in the except block. Python returns the following error (NOT exception):

Traceback (most recent call last):
    File "test.py", line 9, in <module>
        ftp.quit()
NameError: name 'ftp' is not defined