Scripting C++/cli with IronPython (Visual Studio 2008 & IronPython 2.6.1)

Even though there has been a lot of talk about IronPython, there has been very little info about how to use it with C++/cli.  I’ve actually found posts claiming that it is not possible to use IronPython with C++/cli.

Well, it is possible and easy, once you have a working example.  If, not then … well, lets just hope your hair will grow back.

Ok, I’m never one to take the easy way out, but I started by creating a C# dll that called my IronPython script and then called the C# dll from C++/cli.  That worked but seemed overly complicated.  If you do not mind a middleman then I guess it is ok, but if you want to go straight from C++/cli to IronPython, read on.

When I first tried to write a call to an IronPython script from  C++/cli, I tried a direct conversion of C# code into C++/cli code.  That didn’t work, so I then tried using RedGate’s .Net Reflector and the C++/cli add-in for .Net Reflector.  This got me 70% there.  Combining both with some trial and error got me the rest of the way. 

Funny, but when you look at the code, it seems so simple – yet getting there was not easy.

So, the following snippet shows a simple usage of IronPython as a scripting language.  It takes the first parameter passed in prints it to the console, passes it to the IronPython script: ipyStrings.ipy, then prints to the console the value of the same parameter that was passed back.  The IronPython code takes the string, prints it, reverses it, then sends it back.

C++/cli code:

Code Snippet

1. int main(array<System::String ^> ^args)
2. {
3.     try
4.     {
5.         if(args->Length>0)
6.         {   
7.             String^ filename = "ipyStrings";
8.             String^ path = Assembly::GetExecutingAssembly()->Location;
9.  
10.             ScriptEngine^ engine = Python::CreateEngine();
11.             ScriptScope^ scope = engine->CreateScope();
12.             ScriptSource^ source = engine->CreateScriptSourceFromFile
13.             (String::Concat(Path::GetDirectoryName(path), "\\", filename, ".ipy"));
14.        
15.             Console::WriteLine(args[0]);
16.  
17.             scope->SetVariable("passedArgs", args[0]);           
18.             source->Execute(scope);
19.  
20.             Console::WriteLine(scope->GetVariable<String ^>("passedArgs"));
21.         }                                   
22.     }
23.     catch(Exception ^e)
24.     {
25.         Console::WriteLine(e->ToString());
26.     }
27.  
28.     Console::ReadLine();
29.  
30.     return 0;
31. }

Python code:

Code Snippet

1. import clr
2.  
3. print "Passed in: " + passedArgs
4. passedArgs = passedArgs[::-1]
5.  
6. print "Sending back: " + passedArgs