DNS query against a specific server using python

Question

socket.gethostbyname sends the DNS resolution query to the DNS server specified by the OS. Is there an easy way to send a query to a *different* server?

I see that twisted.names allows you to do this, but, having all of twisted as dependency to my project when all I need to do is a simple DNS query seems a bit extreme. I also found pydns, but that looks fairly outdated and unmaintained.

Answer 1

there is a dns modul for Python (I don't know is it part of standard Python library or not), on most Linux distribution you can find it, eg. in Debian it's called python-dnspython.

It can handle different nameserver, than OS knows - here is a sample code:

import dns.resolver

r = dns.resolver.Resolver()
r.namerservers = ['127.0.0.1']
# or any other IP, in my case I'm using PDNS, which have two
# parts: a recursor and a resolver; recursor allows requests only
# on localhost

mxservers = r.query("python.org", 'MX').response

Comments

Indeed, this looks much nicer than both twisted or pydns. I think I'll go with that one. Thanks....

Answer 2

It isn't pure python, but you would be pretty much guaranteed a maintained solution if you use the name server lookup in your OS. Something like:

 import subprocess
 nsl_reslt = subprocess.Popen(['nslookup', '' ],stderr = subprocess.PIPE, stdout = subprocess.PIPE).communicate()[0]

Hope this helps,

Comments

I had this option in mind, but opening a subprocess for something as small as this seemed a bit error-prone. If something on the system changes, nslookup replaced by dig or nslookup output changes for example your application will bug out.

Granted, the chance of this happening is slim, but using a fixed-version dependency in your setup script gives you a much safer solution IMO.

I know I may be splitting hairs. Any of the mentioned solutions are fine. But I am curious to see if something like this is not yet implemented in a more standard way. I was surprised to see that ``gethostbyname`` does not take an optional parameter for this task.

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gethostbyname is a simple function with not much flexibility. (You can't, for instance, look up a TXT record.) For anything more complex, you want a proper DNS implementation.

There are a few Python DNS modules. It means adding another dependency, but perhaps not as large as twisted. And of course, you could always manually send UDP packets and listen for responses, but that seems a little unnecessary :)