Book Review: CherryPy Essentials
A little over a week ago I received a review copy of Sylvain Hellegouarch’s new book, CherryPy Essentials, published through Packt Publishing. The timing couldn’t have been better, since we have begun investigating Python web application frameworks at work for a new project. From previous work I have done with TurboGears, I knew that CherryPy was a contender, so I was definitely interested to see what version 3 had to offer. Sylvain’s book is is a good starting point for the information I wanted.
CherryPy Essentials is a fairly short book (251 pages), especially given the breadth of topics it covers. It could easily have been 2-3 times as long, if the author was wordy or repetitive, but the concise writing style means that there is a lot of good information packed into this short volume.
The outline is fairly typical for tech books:
- What is this thing and why do I care? – chapter 1
- How do I get it? – chapter 2
- What can it do? – chapters 3-4
- Build an example app – chapters 5-7
- Advanced topics – chapters 8-10
The real substance of the book begins with chapter 3, which gives an overview of CherryPy. It includes a moderately sized introductory application which lets different authors post notes on a page. The sample code includes embedded comments and is used as a basis for a brief description of how CherryPy decides what to do when an HTTP request is received.
CherryPy comes with a host of modules to make building your application easier. The coverage given these modules in the “Library” section of chapter 3 probably does not do them justice. The author clearly states that his intent is not to create a reference guide, but I would have liked to see this section pulled out into its own chapter and expanded, possibly combined with the Tools list in chapter 4.
The more in-depth discussion of CherryPy in chapter 4 includes instructions for running multiple HTTP servers; various mechanisms for dispatching URLs to Python functions; serving static content; hooking into the core to add your own middleware (or “Tools” in CherryPy-parlance); and WSGI support. The same chapter also includes a description and concise example of how to use each Tool provided in the CherryPy core distribution, following a format not unlike the one I use for my Python Module of the Week series.
Chapters 5-7 discuss the design and development of a photo blog application, which is small enough for the reader to follow but large enough to delve into the details of how to build a real application with CherryPy. The presentation begins with the data model, then covers web services and user interface topics.
Some of chapter 5, which discusses working with databases, is unfocused and includes sections on topics such as backgrounds on database types and object-relational mapping libraries not actually used in the example applications. This material could have been eliminated without serious loss. It is interesting, but it detracts a bit from the overall coherence of this book. Once he selects the Dejavu ORM, the discussion refocuses and covers the mechanics of using that library to store and retrieve data.
Chapter 6 provides an excellent discussion of web services, REST, URL design, and the Atom publishing protocol. These were perhaps the most interesting sections in the book. The author clearly has a great deal of experience to share on these topics. I hope there is another book coming soon with a greater examination of these topics.
The coverage of presentation layer topics in chapter 7 begins with a brief history of HTML, up to the development of DHTML. Then the Kid templating language is introduced (thankfully without a comprehensive survey of all available Python templating languages :-). The UI for the example application is fairly simple, so only basic Kid features are really covered, but that is enough. The more complex DHTML work is handled by Mochikit, introduced here and used more extensively in chapter 8, which is devoted to Ajax.
The last 2 chapters of the book cover topics too frequently left out of other books: Testing and Deployment. The chapter on testing presents several tools which integrate well with CherryPy for automated testing of different aspects of your application, including webtest for unit testing, FunkLoad for load testing, and Selenium for UI testing. I had never seen these tools before, and the descriptions and examples were enough to make me add them to my “to be researched” list.
The final chapter covers deployment options for moving a CherryPy app into production. Options for using Apache, lighthttpd, WSGI, and SSL are covered, but no definitive “best practice” is suggested. I suppose the final choice should be made on more variables than could really be covered, but I would have liked to see clear guidelines for making a decision about which configuration to use in different situations.
Any good, modern, open source project does not stand alone, and CherryPy is no exception. “CherryPy Essentials” makes it clear that integrating with third-party tools is an important part of the design for CherryPy. Tools covered include:
- DejaVu – database access, ORM
- Kid – HTML templating
- FunkLoad – load testing
- Selenium – UI functional testing
Other tools are also mentioned, but covered in less detail.
CherryPy Essentials packs a surprising amount of information into a small space. The coverage is not exceptionally deep in any one area, but is fairly complete. The sample code is consistent and easy to read. The book is full of useful and interesting information and, while it occasionally suffers from disjoint flow, I can definitely recommend it to any Python programmer interested in the future of CherryPy development, and web technologies in general.
Special thanks to Ms. PyMOTW for proof reading this post for me.