I had a really good time adapting Karpatny's blog post to python myself but it didn't give me sufficient understanding so i continued with [1], then [2] and finally deciphering [3].

[1] https://mattmazur.com/2015/03/17/a-step-by-step-backpropagat... [2] http://peterroelants.github.io/posts/neural_network_implemen... [3] https://iamtrask.github.io/2015/07/12/basic-python-network/