Is there any way to get a list of IPs connected to a network? I'm trying to build lots of networking tools so.
Even though RFC 1122 requires any host on the network has to process an echo-request and issue an echo-reply in return it's well known that 'paranoid' people think of ping as an security risk and therefore decline to answer echo-request. So obviously no answer is no definite proof of any given host not being online.
However maybe you want to investigate
nmap and the python libs that make use of it.