I'm using the socket.makefile method to create a file-like object on a UDP socket for the purposes of reading. When I receive a UDP packet, I can read the entire contents of the packet all at once by using the read method, but if I try to split it up into multiple reads, my program hangs.

Here's a program which demonstrates this problem:

import socket
from sys import argv

SERVER_ADDR = ("localhost", 12345)

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
sock.bind(SERVER_ADDR)
f = sock.makefile("rb")

sock.sendto("HelloWorld", SERVER_ADDR)

if "--all" in argv:
    print f.read(10)
else:
    print f.read(5)
    print f.read(5)

If I run the above program with the --all option, then it works perfectly and prints HelloWorld. If I run it without that option, it prints Hello and then hangs on the second read. I do not have this problem with socket.makefile objects when using TCP sockets.

Why is this happening and what can I do to stop it?