how to lock a file in ftp site

[muttu2244 at yahoo.com]

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.

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

regards
yogi