I disagree. In Python, the PEP8 standard is to use snake case for variables and function names. Classes should appear in this format: ClassName. Downey uses the class style for functions because, according to him, he feels it would be too inconvenient to do it the right way. This is a lazy cop-out. If you're writing a book targeting the Python community you should adhere to the Python PEP8 standards out of respect for your readers, if nothing else. The parent poster poses a valid question and it most definitely adds to the conversation because it calls into question the author's respect for his audience.

How is what Downey did any different from me writing a book and stating that correct spelling, grammar, and editing would be too inconvenient for me, so I'm just going to type whatever I feel like and that should be OK, because I addressed my lack of quality and attention to detail during my introduction?

By the way. Thanks for commenting.