IronPython in Action

by Michael Foord and Christian Muirhead (2009)

Disclaimer: I'm friends with both the authors and was sent a freebie review copy by the publisher, so I'm bound to be breathlessly gushing in this review. Fortunately, that's easy to do, because the book really is great. (Except for Christian's chapters... Joke!)

Having spent some years working with .NET, and with a series of intriguing personal experiments in Python under my belt, I originally approached IronPython some years ago with a modicum of trepidation. I feared that the weld between the two would be intrusively visible, forming distracting differences from regular Python. I feared for the execution environment, the data types, and perhaps even the syntax itself.

Experience with IronPython showed these worries were needless. I have found IronPython to be a remarkably pleasant marriage - the same elegant language we know and love, given first-class status in the .NET runtime. Gifted with seamless interoperability with other .NET languages, the dowry from such an alliance turns out to be all the .NET libraries in the world, including the substantial and highly capable .NET standard libraries themselves.

IronPython is, to some extent, a niche implementation of a niche language. However, its position seems to potentially be one of importance and strength. Not only does it allow Python programmers to use .NET libraries - and does so admirably, but it also allows the existing legions of .NET programmers to be introduced to the joys of Python. They will fall in love with it, and will be able to introduce it into their workplaces in a way that is politically acceptable. After all, it is now simply another .NET language. Since .NET is orders of magnitude more popular than Python, this could turn out to be an important source of future Python adoption.

This book is aimed to satisfy programmers coming from both the Python and the .NET worlds, and in this it seems to succeed. It starts with quick overviews of concepts from each: 30 pages about Python as a language, and 17 pages about .NET as an environment (data types, events, delegates, Windows Forms, etc) - just enough to get everyone up to speed regardless of background, but without being so verbose as to turn anyone off with a surfeit of material they are already familiar with. Despite being brief, these sections are packed with detail and very pragmatic, focusing on real-world use such as inheriting from existing .NET types, and solving some common problems like creating Windows Forms applications from IronPython.

This style of practical and dense informative content is continued throughout. Straight after the opening sections, we dive right in with another rapid-fire chapter, demonstrating common IronPython techniques by writing a non-trivial application. Woven around this ongoing example, the chapter discusses many immediately important topics, including duck typing, Python protocols, MVC, using Windows Forms to build a GUI, tab pages, dialogs, menus, toolbars, images, saving text files, .NET Streams, text file encodings, Python exceptions and lambda functions. These diverse topics are covered rapidly but thoroughly, giving the reader enough information about each to be able to use them together from IronPython to create a useful project.

Having covered these foundations, the book then moves on to address some specific areas in more detail. The following chapter headings give you some idea of the topics which are explored in depth:

• First-class functions in action with XML - demonstrates pragmatic use of functions as first-class objects, and higher-order functions (functions that take other functions as arguments and return modified versions.) and of course decorators. These are shown in use, appropriately paired up with the .NET XmlWriter and XmlReader classes, demonstrating event driven parsing of XML.
• Properties, dialogs and Visual Studio - Python properties, .NET dialogs, and using IronPython in Visual Studio. This sounds like a straightforward chapter, but as you might guess, the book gets deep into the topics and is jammed full of information. By the end of the chapter you'll have added to the example application to create document observers, used BinaryFormatter to serialise objects, and touched on Python's pickle equivalent.
• Agile Testing: where dynamic typing shines - From the unittest module and creating tests, through mock objects, listeners, monkey patching, dependency injection and functional testing. This is a dense chapter in a dense book, touching along the way on Python attribute lookup rules, bound and unbound methods, asynchronous execution for functional testing. My only criticism is that it's clearly hard for developers to 'get' testing until they have hands-on experience of it, so this single-chapter, while very thorough in explaining how to test, has an ambitious remit, and doesn't have enough space to explain much of why we test. I guess this is partially my own bias shining through here - I regard testing as quite literally the most important thing to happen in computer science since the invention of the compiler, and would encourage anyone interested to go and read as much as they can about it.
• Metaprogramming, protocols and more - More Python protocols, dynamic attribute access, and metaclasses. The sorts of things that in a static language would be deep black magic, or else completely impossible, but here they are just the right sort of crazy. Read, enjoy, and unlearn. We see how to create a profiling decorator, that modifies the functions you pass to it, wrapping them in stopwatch timing calls. We also learn about some of the more advanced integration of IronPython with the .NET CLR, including static compilation of IronPython code into assemblies, and one of the very few additions to Python syntax that IronPython has been obliged to provide - the typing of .NET arrays and generics. You'll never need to use generics yourself (in Python, everything is a generic), and you'll never want to go back to typed containers if you can avoid it. However, you may need to deal with some from an existing C# API, and this is how you do it.

Whew! We're only halfway through! The remaining chapters are equally detailed, but I'm going to start skimming through them somewhat. They cover the interactions of IronPython with more advanced .NET topics such as:

• Windows Presentation Foundation (WPF) and IronPython - WPF is the DirectX user interface library that is a successor to Windows Forms. This includes XAML, an XML dialect for describing user interfaces, decoupling their implementation from application logic.
• Windows System Administration with IronPython - using IronPython as a scripting language for sysadmin automation tasks, from the simple, such as copying files, to the complex, such as Windows Management Instrumentation (WMI), administration of remote machines, and a substantial discussion on the uses of PowerShell with IronPython.
• IronPython and ASP.NET - building a web-based front end to the sample application developed earlier. Reusable controls.
• Databases and Web Services - using ADO.NET to work with databases, and using SOAP and REST.
• Silverlight: IronPython in the browser - creating Silverlight applications, and accessing the browser DOM from them.
• Extending IronPython with C#/.NET - all about creating C# class libraries for use in IronPython, calling unmanaged code from IronPython, and creating interfaces on your C# classes to provide dynamic, Pythonic behaviour. It also includes dynamic compilation of assemblies at runtime, which opens the door to advanced code-generation techniques.
• Embedding the IronPython Engine - many developers might want to provide IronPython as a scripting language within their own application, and this chapter shows you how.

Alright, that's it! There are appendices:

• A whirlwind tour of C# - in case anyone wants more guidance while looking at some of the C# code or concepts that are discussed throughout the book.
• Python magic methods - a description of all the Python magic double-underscore methods, which is a fabulous resource, one which l haven't seen collected anywhere else, and have been referring back to ever since I read the book.

So there you have it. If you haven't inferred already, I learned absolutely heaps from this book, even though it's about a language and environment I've been using every day for years. I think I can say without any equivocation that this is the best IronPython book in the world. If you're a .NET person who is curious about Python (and believe me, you should be), or if you're a Python person who fancies .NET - maybe for DirectX or Silverlight or any number of other wonderful things, then you should absolutely go directly to the IronPython in Action book website right this second and buy it.

What are you still doing here?

Update: Good catch Carl, I forgot the all-important rating!

10/10 if you already use, or are curious about using, IronPython - then you need this book.

0/10 if dynamic languages make you break out in hives, or if .NET makes you think of Darth Vader, then you shouldn't touch this book with a barge pole.