I got responses from a posting (requesting test readers) on a German Python Forum:
Many responses, but all responses were high-quality. Now i have time to apply the proposed changes into The Python Game Book. My secret dream that my test readers would do the work for me and simply apply the edits in the wiki did not come true (yet).
Most important: i get rid (again) of the line numbers in Python code.
Background: The Python programming language does not use line numbers, but in most computer books line numbers are necessary to explain code sinppets.
I found a dokuwiki-plugin that allowed client-controlled line number toggling. However, the plugin made the code look very ugly and i could not fix this ugliness.
Now i'm back to a less sophisticated plugin with only server-controlled line number toggling. But the code looks better readable. And thanks to a very detailed line-by-line discussion after each code sinppet, i hope to make the book readable without ever using line numbers at all.
see here a page with code examples in full beauty: