Book Review: Porting to Python 3
Lennart Regebro sent me a copy of his Porting to Python 3 following PyCon 2011, and now that work on my own book is nearly complete I was finally able to sit down and study it. I have two major Python 3 porting projects ahead of me soon, and I hoped that Lennart’s book would guide those projects. I was not disappointed.
Quick Review
Inspired by Gene Ambaum and Bill Barnes’ review short-cuts, here’s my review for the impatient reader:
Why I picked it up: I am preparing to port PyMOTW to Python 3 and we are starting to study what it would take to make the switch at work, too.
Why I finished it: At a computationally pleasing 128 pages, the book gets right to the point, without a lot of fluff and filler.
I’d give it to: Developers with enough Python 2 code that porting to version 3 is going to be a major project. Programmers who want to support both 2 and 3 at the same time will also find helpful information.
Python 2 vs. 3
The Python community is in an interesting period of change. Major development of Python 2 has stopped with release 2.7, but there are still a lot of developers out in the world using it as their primary tool. The number of packages available under Python 3 continues to grow steadily, but there is still a lot of legacy code to be ported, supported, or simply cut off. Lennart Regebro’s new book, Porting to Python 3, is a guide for those of us who have not yet completed our transition. It covers the options for supporting Python 3, either concurrently or exclusively, and includes guidance about choosing the best approach for your project.
Just the Facts
While there is a lot to like about Porting to Python 3, the two aspects that stand out are the size and the organization of the content. The author does not beat around the bush or belabor his point. His writing is clear and concise, resulting in a slim handbook that can be given to a manager who needs to understand the ramifications of moving from Python 2 to Python 3, while still containing enough detail to be used by a developer for reference during the porting process.
The author does not beat around the bush or belabor his point.
Strategies for Successful Migration
The material in the book is organized in exactly the way you need to digest it. The first chapter is a quick explanation of what Python 3 is, with guidance for deciding when, and whether, to make the switch. Chapter two covers strategies for migrating, either all at once or during installation so that both Python 2 and 3 can be supported with the same code base.
Next, the author helps you prepare for the porting effort by providing tips for bringing your code into the best beginning state. He covers the process for staging the migration by getting the code to run correctly under Python 2.7, possibly with a compatibility layer so that the same source can run under Python 3 as well.
The author helps you prepare by providing tips for bringing your code into the best beginning state.
Chapter 4 introduces 2to3, the primary tool for automatically porting Python 2 code to run under Python 3. 2to3 supports a large number of conversions, but no automatic solution is going to be perfect, so chapter 5 explains how to address the most commonly found cases where the tool may have made the wrong decision or where it could not translate the code at all.
Chapter 6 lists the cases where using more “modern idioms” will either make the code easier to maintain for both Python 2 and 3, or make it run more cleanly under Python 3.
Advanced Topics
The rest of the chapters are about more advanced topics, including techniques for supporting Python 2 and 3 without using 2to3; changes in the C API that affect extension modules; and customizing 2to3 to handle cases that appear in your code, but are not common enough to already be addressed by the core library.
Handy Reference
The appendices provide concise reference list of common porting issues and their solutions, so it is not necessary to search the entire book for a fix when you encounter a problem. There is also a list of the standard library modules that have been renamed or otherwise reorganized, something I will find especially useful while working on PyMOTW.
Conclusions
Porting to Python 3 is self-published, and that shows in some of the rough edges. But those do not detract from the value of the information and advice that it contains. I recommend it for developers preparing to migrate their code base, especially if there is enough code to make it a major project. Programmers who want to support both 2 and 3 at the same time will also find helpful information.
Sample Chapter
The website for the book has chapter two, Migration Strategies, available for free.
Disclaimer: I received a free review copy of this book from the author.