I had a problem where my scripted FTP uploads through ftplib in Python 2.3 would experience long (6 or 7-second) delays before transferring each file. Other FTP programs were fine, except for a similar delay on connect. It turned out to be an interaction with ftplib’s IPv6 support in Python 2.3 and the Mac OS X name resolver, and it finally appears to be fixed in the recently-released Mac OS X 10.3.8, which noted speed improvements in certain network applications.
In case the delay bites anyone else (or in case it’s not really fixed, and some other network change is just fooling me) here’s the workaround I’ve been using until now.
With IPv6 support in Python 2.3 / Mac OS X 10.3, ftplib’s ntransfer function now calls getaddrinfo for every single file tranferred, and the name resolver does a slow timeout each time. Making a local copy of ftplib and replacing the call to getaddrinfo with constants may be ugly, but it worked around the problem.
Original line (multi-second delay), at ftplib.py line 233:
af, socktype, proto, canon, sa = socket.getaddrinfo(host, port, 0, socket.SOCK_STREAM)
Changed line (assumes IPv4 addresses):
af, socktype, proto, canon, sa = (2, 1, 6, '', (host, port))
This change speeds up multi-file FTP transfers immensely (at least to my FTP server) under Mac OS X 10.3.0 through 10.3.7, but early results indicate it’s not necessary on 10.3.8.