#5 got me after almost three decades of programming in various languages. I initialized a future in the argument list, but the second time I called the function

#5 got me after almost three decades of programming in various languages. I initialized a future in the argument list, but the second time I called the function, python told me I set the result of the future twice. AFAIK no language behaves this way. Rest of the points I was already familiar with from various experiences. To me, they are just filler for the article.