IronPython DLR; passing parameters to compiled code?

Question

I'm currently doing the following to create and execute a simple python calculation, using DLR:

ScriptRuntime runtime = Python.CreateRuntime();
ScriptEngine engine = runtime.GetEngine("py");

MemoryStream ms = new MemoryStream();
runtime.IO.SetOutput(ms, new StreamWriter(ms));

ScriptSource ss = engine.CreateScriptSourceFromString("print 1+1", SourceCodeKind.InteractiveCode);

CompiledCode cc = ss.Compile();
cc.Execute();

int length = (int)ms.Length;
Byte[] bytes = new Byte[length];
ms.Seek(0, SeekOrigin.Begin);
ms.Read(bytes, 0, (int)ms.Length);
string result = Encoding.GetEncoding("utf-8").GetString(bytes, 0, (int)ms.Length);

Console.WriteLine(result);

Which prints '2' to the console, but;

I want to get the result of 1 + 1 without having to print it (as that seems to be a costly operation). Anything I assign the result of cc.Execute() to is null. Is there any other way I can get the resulting variables from Execute()?

I am also trying to find a way to pass in parameters, i.e. so the result is arg1 + arg2 and have no idea how to do that; the only other overload for Execute takes ScriptScope as a parameter, and I've never used python before. Can anyone help?

[Edit] The answer to both questions: (Desco's accepted as pointed me in the right direction)

ScriptEngine py = Python.CreateEngine();
ScriptScope pys = py.CreateScope();

ScriptSource src = py.CreateScriptSourceFromString("a+b");
CompiledCode compiled = src.Compile();

pys.SetVariable("a", 1);
pys.SetVariable("b", 1);
var result = compiled.Execute(pys);

Console.WriteLine(result);

desco · Accepted Answer · 2011-01-31 15:09:13Z

6

You can either evaluate expression in Python and return its result (1) or assign value to some variable in scope and later pick it (2):

    var py = Python.CreateEngine();

    // 1
    var value = py.Execute("1+1");
    Console.WriteLine(value);

    // 2
    var scriptScope = py.CreateScope();
    py.Execute("a = 1 + 1", scriptScope);
    var value2 = scriptScope.GetVariable("a");
    Console.WriteLine(value2);

answered Jan 31, 2011 at 15:09

desco

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Comments

Jon Skeet · Accepted Answer · 2023-07-01 15:09:05Z

3

You definitely don't have to print it. I'd expect there to be a way of just evaluating an expression, but if not there are alternatives.

For example, in a dynamic graphing demo I wrote a long time ago (and unfortunately no longer have the code for) I created a function, using the python:

def f(x):
    return x * x

and then got f out of the script scope like this:

Func<double, double> function;
if (!scope.TryGetVariable<Func<double, double>>("f", out function))
{
    // Error handling here
}
double step = (maxInputX - minInputX) / 100;
for (int i = 0; i < 101; i++)
{
    values[i] = function(minInputX + step * i);
}

You could do something similar if you want to evaluate the expression multiple times, or just assign the result to a variable if you only need to evaluate it once.

edited Jul 1, 2023 at 15:09

answered Jan 31, 2011 at 15:10

Jon Skeet

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2 Comments

Aron Over a year ago

The example link is broken

Jon Skeet Over a year ago

@Aron: Yup, unfortunately I think that was in the 2nd edition, and I lost the code when updating the site. (I've a suspicion that it didn't work fully with later versions of the DLR, but it's a long time ago.)

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