Hi,
What is a Good Book or Tutorial for Wordpress Theme Development?
Here is a Udemy course on sale for 10.99 normally 175.00 (in four days) on theme development with Bootstrap.
https://www.udemy.com/bootstrap-to-wordpress/
Some Books:
Some more books here. The are old but there is probably useful information in them that can be adapted.
https://ebooks-it.org/1430259140-ebook.htm
I would invest in Digging Into Wordpress and the Tao of Wordpress. Worth the investment.
Cheers,
Vince
2 Likes
Cheers for that!
oh, how i miss
http://it-ebooks.info
when you could download from there
I have that course too… I really should get on with it.
Cheers for the reminder 
And here is a rather out of date book but A LOT of the principles remain the same…
just the code/ codex … stuff will need re doing, so might drive you nuts.
however, its free…
oh and a few months too late too probably but HEY!
did I mention its free?
The best out of date things are worth waiting for 
I think my version is from something like 2010 … ouch, but you might find some useful stuff in it