how to lock a file in ftp site

[Steve Holden]

Ben Hutchings wrote:
> <muttu2244 at yahoo.com> wrote:
> 
>>hi all
>>
>>am trying to write some information into the file, which is located in
>>ftp, and this file can be updated by number of people, but if at all i
>>download a file from the ftp to my local machine, update it and then
>>upload it back to ftp, and at the same time if some one else downloads
>>the same file for the modification, then the data will be overwritten.
>>
>>so is there a way in Python script where i can lock the file, so that
>>no one updates it until i release the lock.
> 
> 
> A common means of cooperative file locking is to use the existence of
> a second file as a lock indicator.  I'm not sure that can be done over
> FTP, though, because I think when you write to such a file you can't
> tell whether it existed previously (which would mean someone else
> owned the lock).
> 
Well of course you could place a lock on the lock file before you tested 
for its presence by creating another file ...
> 
>>Or is there a way where i can directly update the file from the ftp
>>itself, i mean without downloading it to my local machine.
>>
>>Thanks in advance for the help
> 
> 
> You should probably switch from FTP to a version control system, such
> as CVS or Subversion.  They don't normally use locking, but they do
> detect conflicting changes and stop you from overwriting other
> people's changes.
> 
I'm not sure a version control system is right for the OP's needs, but 
clearly unadorned FTP isn't going to hack it either.

This being the Python, of course, it would be relatively simple to 
design a protocol that would provide the required functionality and then 
build clients and servers for that protocol. But we don't know whether 
that's an option yet.

regards
  Steve
-- 
Steve Holden       +44 150 684 7255  +1 800 494 3119
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