Why doesn’t dnspython implement the resolv.conf fallback to “the name server on the local machine”?

[singhpta]

resolv.conf man-pages (ref) state that if no nameserver entries are present, the default is to use “the name server on the local machine.”

dnspython instead raises NoResolverConfiguration when no nameservers are configured.(code)

My understanding of the name server on the local machine. is that for linux systems we can largely fallback to 127.0.0.1. Before proposing any changes though, I’d like to understand whether the current implementation is:

• an intentional design choice due to portability / correctness concerns, or
• a deliberate deviation from resolv.conf semantics because the fallback is underspecified in modern systems

cc: @prashantpcm94

[rthalley]

I think this is an oversight rather than a purposeful design decision on my part. Generally speaking there isn't a nameserver on 127.0.0.1 port 53 so it's not a very useful fallback, so dnspython's behavior, even if wrong, may be more practical. I'll have to ponder whether it is worth changing, and what the backwards compatibility implications would be.

[rthalley]

Oh, and also generally if there is a nameserver on 127.0.0.1 port 53, people explicitly configure it in the resolv.conf rather than relying on the fallback, since I suspect many people do not know of the fallback even though it is clearly documented as you said, and has been that way since at least 1999 (I only looked back that far).