Partial download with ftplib and retrbinary

Giampaolo Rodola' gnewsg at
Fri Jun 6 16:23:31 CEST 2008

On 24 Mag, 12:53, fepeac... at wrote:
> I am breaking/interrupting my connection with theftpserver at
> present when doing a partial download of a file. I have a callback
> with retrbinary that raises an exception and ends the download. The
> problem is that the server is not notified and hangs. I cannot send
> any further commands and need to relogin to download further. Is there
> a way to still continue downloading without having to login again.
> My retrbinary function is:
> ftp.retrbinary('RETR '+file, handleDownload,1,bound[0])
> where bound[0] is an integer specifying the start byte of the
> download.
> My callback is:
> def handleDownload(block):
>     global count,localfile,number
>     localfile.write(block)
>     if count==number:
>             raise(Exception)
>     count=count+1
> where number specifies the number of bytes to download.
> Help would be gratefully received.

The server hangs on because the data connection is left open.
Unfortunately you have no easy way to close the data connection by
using retrbinary.
You have to trick a little bit and keep a reference of the data socket
and manually close it.
The example below starts to retrieve a file and stops when 524288
bytes have been received.
Hope this could help you.

import ftplib
ftp = ftplib.FTP('', 'user', 'password')
ftp.voidcmd('TYPE I')
conn = ftp.transfercmd('RETR filename') # the data socket
bytes_recv = 0
while 1:
    chunk = conn.recv(8192)
    # stop transfer while it isn't finished yet
    if bytes_recv >= 524288: # 2^19
    elif not chunk:
    bytes_recv += len(chunk)

--- Giampaolo

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