C# 4 and .NET 4

302 ❘ ChaPTer 12 dynAmic lAnGuAGe extensiOns
The code defines a section for “microsoft.scripting” and set a couple of properties for the IronPython
language engine.
Next, you get a reference to the ScriptEngine from the ScriptRuntime. In the example, you specify that
you want the Python engine, but the ScriptRuntime would have been able to determine this on its own
because of the py extension on the script.
The ScriptEngine does the work of executing the script code. There are several methods for executing
scripts from files or from snippets of code. The ScriptEngine also gives you the ScriptSource and
ScriptScope.
The ScriptSource object is what gives you access to the script. It represents the source code of the
script. With it you can manipulate the source of the script. Load it from a disk, parse it line by line, and
even compile the script into a CompiledCode object. This is handy if the same script is executed
multiple times.
The ScriptScope object is essentially a namespace. To pass a value into or out of a script, you bind a
variable to the ScriptScope. In the example, you call the SetVariable method to pass into the Python
script the prodCount variable and the amt variable. These are the values from the totalItems text box
and the totalAmt text box. The calculated discount is retrieved from the script by using the GetVariable
method. In this example, the retAmt variable has the value you’re looking for.
In the CalcTax button you look at how to call a method on a Python object. The script CalcTax.py is a very
simple method that takes an input value, adds 7.5 percent tax, and returns the new value. Here’s what the
code looks like:
def CalcTax(amount):
return amount*1.075
Here is the C# code to call the CalcTax method:
private void button2_Click(object sender, RoutedEventArgs e)
{
ScriptRuntime scriptRuntime = ScriptRuntime.CreateFromConfiguration();
dynamic calcRate = scriptRuntime.UseFile("CalcTax.py");
label6.Content = calcRate.CalcTax(Convert.ToDecimal(label5.Content)).ToString();
}
A very simple process. Again you create the ScriptRuntime object using the same configuration settings
as before. calcRate is a ScriptScope object. You defined it as dynamic so you can easily call the CalcTax
method. This is an example of the how the dynamic type can make life a little easier.
dynamiCobjeCT and eXPandoobjeCT
What if you want to create your own dynamic object You have a couple of choices for doing that, by
deriving from DynamicObject or by using ExpandoObject. Using DynamicObject will be a little more
work because you have to override a couple of methods. ExpandoObject is a sealed class that is ready
to use.
dynamicobject
Consider an object that represents a person. Normally, you would define properties for the first name,
middle name, and last name. Now imagine the capability to build that object during runtime, with
the system having no prior knowledge of what properties the object may have or what methods the
object may support. That’s what having a DynamicObject-based object can give you. There may be
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