This observation about the poor quality of their books and their shady practices has been noted by many others as well. I am not saying all of them are bad but certainly the majority of them are. See these discussions:
https://www.quora.com/Why-are-the-books-from-Packt-Publishin...
https://forum.unity3d.com/threads/so-i-got-contacted-by-pack...
I have not read the particular Python book you are referring to but I have viewed many many other Packt Publishing titles and they are almost always poor and unacceptable quality. The reasons are what I stated earlier about poor English, typos, not spell-checked, bad grammar and often simply little more than paraphrasing official documentation.
I consider publishers like Pragmatic, Oreilly or Manning to be examples of reputable publishers. Packt comes nowhere near this level of quality or professionalism.
>"However, just as HN tries to provide value by best effort quality ranking, PythonBooks also makes a best effort attempt at judging quality. It is not perfect, but it's the best I could do."
I really don't think there's any substitute for judging a technical book solely by the content presented in it.