IronPython and LINQ: A Devlink Correction

During my “Anatomy of an IronPython Application” presentation at Devlink, I mistakenly said that LINQ can be consumed from IronPython easily. I said this because I was thinking that IronPython 2.6 was built using .NET 3.5 when in fact it’s built with .NET 2.0. Fortunately, if you want to use LINQ, you still can because .NET 3.5 is really .NET 2.0 plus extensions; you just have a bit of extra work to do. First on the todo list is to copy the System.Core.dll for 3.5 to some other location (I was able to get to it from it’s home in the c:\windows\assembly directory) and then use the “clr.AddReferenceToFileAndPath” in your IP code to gain access. Then, with a simple import of the Enumerable or Queryable type, you magically have access to LINQ.

Still, the story doesn’t end there. You have to remember that IronPython does NOT support extension methods and since LINQ is pretty much a collection of extensions methods, there’s a problem. Why this design decision? Because in order to support extension methods, the IronPython team would have had to make changes to the core language which would have, of course, been rather un-Pythonic. This means that the code for consuming LINQ is going to be somewhat messy. The following snippet gives an example of consuming the Average function of the Enumerable object.

clr.AddReferenceToFileAndPath(r"C:\folder\System.Core.dll")
from System.Linq import Enumerable
from System import Func

list = [1,2,3,4,5]

print Enumerable.Average[object](
    list, Func[object, int](lambda x:x))

I have a lot of concerns as soon as I see “object” and “int” in brackets. At this point I’m going to hold save those concerns until my next post. Instead I’m going to leave this as an example of consuming LINQ from IronPython.

I should point out that Harry Pierson’s post on IronPython and Linq-to-XML really got me started on this topic. I also have to give a shout-out to Chris Smith who was kind enough to help me out and relay a couple of CodeMash stories at the same time.