Saturday, July 19, 2008

easier python evaluation from C#

I really like IronPython.

My part of our project is almost completely python, and it both uses and is used by C#.
Using C# from python is almost completely natural. On rare occasions you need to manually resolve a tricky method overload or something of the sort, but generally it's really a joy.

Allowing C# code to call the python code is not so much fun. Somewhere down the road it's supposed to be much better but for now my experience has been that you can do things, but in a lot of cases it's somewhat of a pain. I'm working with IPy 1.x, but from what I gather on mailing list IPy 2.0 hosting might be more abstract at the expense of simplicity.

Anyway, I just came up with a simple extention method for PythonEngine which I think makes things a bit nicer in many common cases. For example, you can write:

object x = engine.Eval("[2*i for i in range({0})",5) // returns [0,2,4,6,8]
object y = engine.Eval("{0}[-1]",x) // returns 8
engine.Eval("{0}.foo(name={1})",pyobj,s) // equivalent to

Here's the code (and here it is again in non-mangled form):

public static object Eval(this PythonEngine engine, string expression_format, params object[] args)
object[] arg_names = new object[args.Length];
Dictionary<string, object> locals = new Dictionary<string, object>();
for (int i = 0; i < args.Length; ++i)
object arg = args[i];
string arg_name = "_cs_arg_" + i; // names should be unique enough not to hide other python names
locals[arg_name] = arg;
arg_names[i] = arg_name;

string expression;
if (args.Length > 0)
expression = string.Format(expression_format, arg_names);
expression = expression_format;

return engine.Evaluate(expression, engine.DefaultModule, locals);

parting thoughts:
* I need to learn how to format code in these blogs
* I need to learn about Curt Hagenlocher's Coils.
* I need to learn about how hosting looks in IPy 2.0
* I really need to get some sleep :-(

1 comment:

Unknown said...

Simple and sweet, can't wait to use it!