cannot enter a bug

"I have tried to follow the instructions on reporting a ubuntu bug as given in https://help.ubuntu.com/stable/ubuntu-help/report-ubuntu-bug.html.en but cannot find any link that allows one to open a new bug."

That document that you referred to and the accompanying one at https://help.ubuntu.com/community/ReportingBugs list several ways to report a bug, but they do not provide a clickable link, because that link need to be different, depending on the package that you want to use as the target for the bug.

How to report bugs in Ubuntu:

1. (preferred way): use the "ubuntu-bug" command

2. create the bug report manually, see https://help.ubuntu.com/community/ReportingBugs#Filing_bugs_manually_at_Launchpad.net

"To file a bug against a specific package you can also use a URL like the following:
(URL removed to avoid using an invalid one)
where PACKAGENAME is the name of the source package about which you want to file the bug report."

In your question description you mention "wx python", so I assume that the bug target has to be wxpython4.0 in Ubuntu.

So the command to run is

ubuntu-bug wxpython4.0

Only in case that this one does not work for whatever reason, then you may use the web interface on
http://bugs.launchpad.net/ubuntu/+source/wxpython4.0/+filebug?no-redirect but you have to expect that you get questions in return to add further information. That information is automatically collected by the ubuntu-bug command, so the ubuntu-command is the preferred way.

This question is not related to the Launchpad hosting services at all, so I am relocating it from "Launchpad" to the "Ubuntu" area.