ipaddress module has no support for scoped IPv6 addresses which prevents the use of ipaddress.ip_address() and ipaddress.IPv6Address() with (always available by default on IPv6 systems) RFC conforming IPv6 link local addresses that specify interface scope. https://tools.ietf.org/html/rfc4007 This is bad because interface scope is required for connect() and bind() operations on multihomed machines, and virtualized or software defined networking will make this case very common. eg. >>> ipaddress.IPv6Address('fe80::dead:dead:beef:ffff') IPv6Address('fe80::dead:dead:beef:ffff') >>> ipaddress.IPv6Address('fe80::dead:dead:beef:ffff%eth0') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ipaddress.py", line 1900, in __init__ self._ip = self._ip_int_from_string(addr_str) File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ipaddress.py", line 1716, in _ip_int_from_string raise AddressValueError("%s in %r" % (exc, ip_str)) from None ipaddress.AddressValueError: Only hex digits permitted in 'ffff%eth0' in 'fe80::dead:dead:beef:ffff%eth0' >>> ipaddress.IPv6Interface('fe80::dead:dead:beef:ffff%eth0') Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ipaddress.py", line 2060, in __init__ IPv6Address.__init__(self, addr[0]) File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ipaddress.py", line 1900, in __init__ self._ip = self._ip_int_from_string(addr_str) File "/opt/local/Library/Frameworks/Python.framework/Versions/3.6/lib/python3.6/ipaddress.py", line 1716, in _ip_int_from_string raise AddressValueError("%s in %r" % (exc, ip_str)) from None ipaddress.AddressValueError: Only hex digits permitted in 'ffff%eth0' in 'fe80::dead:dead:beef:ffff%eth0'