Hi, I started testing a program today which imported twisted.names.client. On every second run, the program didn't return from the import and hung for some time (until I pressed some key, strange...). Turns out, that I don't have Crypto installed and twisted.protocol.dns then tries to read 2 bytes from /dev/random, /dev/srandom, and /dev/urandom (in that order, until first success) in order to determine a random source. If it succeeds with one of those devices, it will also use that method later to read a random integer. The man page for urandom (on linux+fbsd) tells me that /dev/random is for 'uses that need very high quality randomness such as one-time pad or key generation' and that reads to /dev/random will block when the entropy pool is empty. In contrast /dev/urandom will not block, but it's output may be analyzed by an attacker ('Knowledge of how to do this is not available in the current non-classified liter­ature'...but then that linux man page is very old...). I suggest that the usage of /dev/random should be stopped. If it doesn't bite you on import, it will do so later, when you're doing lots of dns request (a coworker of mine had written http crawler and told me, that it started getting slower after 3 hours or so, guess that was the time when /dev/random ran out of entropy). After all, when none of those devices is available, the code will also fallback to using random.randint. - Ralf