Wait... so if you buy book then it seizes to be GPLed? This is quite confusing. For DL research, most code is MIT licenced and legal folks at many industrial labs would be quite hesitent to permit use of code from this repo with feels like legal minefield with different restrictions spread over multiple places including LICENSE, README, fastai website and perhaps printed book. I would highly recommand converting to one simple MIT license and call it a day (except for markdown cells).
I don't get this perspective about the GPL. Look, they are giving you something for free, including the source code and the right to build upon it and publish modified versions. You can do basically whatever you want with it, as long as you pass on the freedoms that were granted to you. Is that unfair? Enjoying getting freedoms but not passing them on is not nice.
I get GPL and fully appreciate its philosophy. The problem happens when you actually use it in practice. Because of its viral nature, anyone with different licensing must convert to GPL if they use your code. For many scenarios, this is actually not possible not just because of commercial secrets but the potential for opening up for security vulnerabilities when you don’t have resources or competitions where you should keep code secret until some time or simply because you have dependencies on other code which is very expensive to get rid off. Due to this reason, many companies forbid the use of GPL licensed software as well as release anything under it (because then you can’t use your own code!). Many other companies simply don't want the headache of checking all of their mess of legacy codebases with a myriad of dependencies that would be hard to untangle into GPL compatible open-source release. The legal and economic overhead when you use or release GPLed code is non-trivial. For this reason, the vast majority of open-source code released by big tech companies on GitHub is MIT/BSD licensed, which ironically is more "freeier" than GPL.
> The problem happens when you actually use it in practice.
I think it's fair for any code publisher to require that the freedoms he/she gives with his/her code never get taken away and it or its modified versions can never get locked up or used in opposition to the wishes and interests of the users (i.e. the users retain the ultimate control over modifying behavior by modifying the code).
> Due to this reason, many companies forbid the use of GPL licensed software as well as release anything under it (because then you can’t use your own code!)
It seems you have a misunderstanding here, and I think it's a common one. You can use your own code in any way you want. You own the copyright, you decide the rules. And you don't need any agreements with yourself. Further, you can release your code to multiple people, each with any license you want. You can also sell proprietary licenses to companies that prefer it, while also releasing the same code under a GPL license to the public.
