Updating to >= 0.7.20 fixes tests on macOS Catalina and newer:
# inet_pton has to be different on Mac OSX *sigh*
assert IPAddress('010.000.000.001', flags=INET_PTON) == IPAddress('10.0.0.1')
> assert int_to_str(0xffff) == '::0.0.255.255'
E AssertionError: assert '::ffff' == '::0.0.255.255'
E - ::0.0.255.255
E + ::ffff