On 08/05/2014 20:06, Chris Angelico wrote: > On Fri, May 9, 2014 at 4:55 AM, Andrew McLean <li...@andros.org.uk> wrote: >> Because of latency in the DNS lookup this could >> benefit from multithreading. > Before you go too far down roads that are starting to look > problematic: A DNS lookup is a UDP packet out and a UDP packet in > (ignoring the possibility of TCP queries, which you probably won't be > doing here). Maybe it would be easier to implement it as asynchronous > networking? I don't know that Python makes it easy for you to > construct DNS requests and parse DNS responses; that's something more > in Pike's line of work. But it may be more possible to outright do the > DNS query asynchronously. TBH I haven't looked into it; but it's > another option to consider. > > Separately from your programming model, though, how are you handling > timeouts? Any form of DNS error (NXDOMAIN being the most likely), and > the sort-of-error-but-not-error state of getting a response with no > answer, indicates that the address is invalid; but what if you just > don't hear back from the server? Will that mark addresses off as dead? > > ChrisA
I've done this on a very small scale in the past. I used http://www.dnspython.org/ to do the heavy lifting. The relevant bits of code looks like: > # Set up the default dns resolver and add a cache > dns.resolver.default_resolver = dns.resolver.Resolver() > dns.resolver.default_resolver.cache = dns.resolver.Cache() and > try: > result = dns.resolver.query(domain, 'MX') > return True > except dns.resolver.NXDOMAIN: > return False > except dns.resolver.NoAnswer: > return False > except dns.resolver.Timeout: > print "*** timeout looking for the MX record for the domain: > %s" % domain > return False You are right, I'll need to do something more sophisticated when I encounter a timeout, but I think that's a matter of detail. Andrew -- https://mail.python.org/mailman/listinfo/python-list