I am thrilled to announce that the second edition of Data Science from Scratch is now available! (buy from Amazon or your other favorite bookstore, or read on Safari, or get a PDF from ebooks.com it looks like.)

It's been almost exactly four years since the first edition came out, and over that time it's helped dozens of people learn data science, Python, or possibly some combination of the two.

However, the first edition used Python 2.7. And as time ticks by, I've been feeling guiltier and guiltier about having a book out there with my name on it that tells people to use Python 2. Because in [current year], you should not be using Python 2. Stop using Python 2!

Eventually I realized that the only way to clear my conscience was to prepare a second edition that advocated for Python 3. Accordingly, the new edition is based on fresh, clean Python 3.6. (Except for a standalone section on dataclasses, which is based on Python 3.7, for obvious reasons.)

But since I was already in there fixing things, I decided to really fix things:

• I cleaned up all the code. I'm a much better coder than I was 4 years ago, and so I spent a lot of time making the examples and implementations cleaner and more readable. (I also removed language features like map and filter and partial that I've since decided are best avoided. Feel free to argue with me about this on Twitter, everyone else seems to.)
• I added an emphasis on using assert statements to test your code, which I wove throughout the book's narrative. I also used a lot more assert statements that didn't appear in the book but that helped me be more confident that the code is correct.
• I used Python-3.6-style type annotations for most of the code in the book. This may strike you as objectionable, as a lot of people don't like type hints in Python. Nonetheless, I decided it was the right choice both morally and pedagogically, so bear with me, and by the end of the book you'll wonder how you ever lived without them. I also used these to help ensure that the code in the book is correct.
• I fixed all the examples that were broken. For example, the O'Reilly store no longer exists, which means that the "scraping the O'Reilly store" example no longer works. I replaced it with an example that involved scraping congress.gov. (Will that site exist in 4 years? Who knows?) I also fixed the Twitter authentication instructions, although there's a good chance they're broken again by now.
• I made many of the examples better. I replaced the janky 8x8 homemade digits in the neural networks chapter with the MNIST dataset. And so on.
• I convinced them to replace all the bit.ly links with the original URLs (you're welcome).
• I added a new chapter on "Deep Learning". Admit it, you want to learn about deep learning! Over the last couple of years I've been doing a livecoding stunt that involves building a deep learning library from scratch in an hour. I adopted that approach into a new chapter (which took a lot more than an hour to write).
• I built on the "deep learning" code to modernize the NLP chapter, adding new sections on word2vec and RNNs.
• Finally, I added a "Data Ethics" chapter, assuming that by the time people get to the end of the book they probably want to know what I think about data ethics.

All that said, on some level it is just an improved, more-modern version of the first edition. If you are a Joel Grus completist (or if you haven't read the first edition) (or if you need a kick in the pants to upgrade to Python 3) (or if you want to learn about type annotations) then you probably want to read it. If you already read the first edition then maybe you'll be happy just poking at the new code on GitHub.

Also, the cover looks extremely different, as O'Reilly has completely changed their design language. So if you are an O'Reilly cover completist you might also want to get it.

Anyway, I am extremely thrilled to share the new edition with you and (in particular) to no longer have a Python 2 book out there with my name on it. (I mean, the first edition is still out there, and I'm sure I'll still be fielding errata about it until the sun burns out, but at least now it's officially defunct.)

Enjoy!