listening on 0.0.0.0 means listen on all IP
addresses on the machine. the IP address 127.0.0.1 is the local loopback device and cannot be connected to from another
machine. While 0.0.0.0 is ok to use if its your machine it
is common to have multiple IP addresses on a server and
in that case listening on 0.0.0.0 would mean no other
server could use port 8000 on any other IP address
for that reason you may want to put the actual
IP address you really want to use in explicitly.
