In the most recent tumbleweed release, running in a freshly installed Anaconda
python environment the following command to start Jupyter Notebook, a local
interactive server popular in data science applications, and accessible via web
browser:

:~> jupyter notebook

returns an error 99 {unable to bind}.

Upon contacting the developers I have been told to perform the following change
in /ETC/HOSTS

BEFORE 

127.0.0.1       localhost
# special IPv6 addresses
::1             localhost ipv6-localhost ipv6-loopback

AFTER 

127.0.0.1       localhost
# special IPv6 addresses
::1             localhost6 ipv6-localhost ipv6-loopback

The problem according to them is that localhost is both the IPV4 and the IPV6
adress, I was told that is not a good practice for IPV6 and IPV4 loop interface
to be called both localhost, as it might break things.

As this is a very basic part of the system, I assume you had a very good reason
to do so, however I want to bring to your attention this incident.

Thank you