Resuming download of a file

This script shows how to resume downloading of a file that has been partially downloaded from a web server. It's been tested with Apache 1.3.x, but should work with any web server that understands the "range" header.

This script uses the extra header - "Range" to let the web server know that we only want a certian range of data to be downloaded. The server must support this, but this is part of the HTTP1.1 spec, so it should be widely supported.

I essentially use the urllib.FancyURLopener to do all the dirty work of adding a new header and doing the normal handshaking. I just had to let it know that the "error" 206 is not really an error - just continue to proceed normally.

I also do some extra checks to quit the download if I've already downloaded the whole file.

Check out the HTTP1.1 RFC to learn more about what the headers mean. The script should probably do a check to make sure the web server accepts "range" but that is pretty simple to do.