I'm writing a django app with a form that accepts an IP and does a whois lookup on the discovered domain names. I've found the Ubuntu package whois which I plan to call from a python subprocess, and read the stdout into a StringIO, then parse for things like Registrar, Name Servers, etc.

My question is, it seems that there are many paid whois services, which means that there must be a reason why people don't just use this Ubuntu package. I'm wondering if there's a request limit on the number of requests from a single IP to the package's whois server? I will probably be making 250 domain lookups per IP or maybe more. Also, I've found that some domains aren't searchable:

qmul.ac.uk is searchable
kat.ph is not searchable 
ahram.org.eg is not searchable 

Any particular reason for that?