Between Python 3.4 (3.4.5 I've tested with) and Python 3.5 (3.5.2), the behavior of ipaddress's subnet() method changed.

This code:

$ cat iat.py
import ipaddress

p = ipaddress.IPv4Network("172.0.0.4/30")
subnets = p.subnets(new_prefix=31)
n = next(subnets)

print(list(n.hosts()))

has two different outcomes on 3.4 vs. 3.5:

$ python3.4 iat.py 
[IPv4Address('172.0.0.4'), IPv4Address('172.0.0.5')]
$ python3.5 iat.py 
[]

AIUI, the 3.4 behavior is the correct one (or the docs need to be fixed).