Lists inside dictionary and how to look for particular value

[mick verdu]

@Peter Otten:

I have lists for keys. What I want is if host already exists it would overwrite otherwise add to database. And if host doesn't exist it will first add this host to database and then compare its IP with IPs of rest of hosts. If ip matches with any of the other hosts, it will delete the host that it just added now.I know it doesn't make sense but I need to do it.