Why is calling CompiledCode.Execute from C# for an IronPython script not behaving as expected

Question

I am trying to call an IronPython (2.7.1) script from C# (4.0)

This is related to IronPython integration in C#: a specific problem/question

I have a python script like below in a file script.py

import clr

def getStream(activity):
    if activity.ActivityType == 'XXX':
        if activity.Complexity == 'LOW':
            return 1
        else:
            return 2
    else:
        return 0

getStream(activity)

I am trying to pre-compile the script and reuse it later

ScriptEngine engine = Python.CreateEngine();
ScriptSource source = engine.CreateScriptSourceFromFile("script.py");
CompiledCode compiledCode = source.Compile();
dynamic scope = engine.CreateScope();
// .. creating an activity object here
scope.SetVariable("activity", activity);

Now to get the streamId if I do this it doesn't work

int streamId = rule.Execute<int>(scope);

The exception is
IronPython.Runtime.Exceptions.TypeErrorException was unhandled by user code Message=expected int, got NoneType

But this will work

rule.Execute(scope);
int streamId = scope.getWorkstream(activity);

My question is what is the correct usage of calling Execute method of the CompiledCode class ?

@sehe rule.Execute<int>(scope); throws an exception like expected int but got null type or something similar. I can later update with the exact exception. If I just do rule.Execute(scope) the object returned is null. — softveda
– softveda, Commented Nov 29, 2011 at 8:03

Jeff Hardy · Accepted Answer · 2011-11-29 16:48:12Z

2

I believe Execute will only return a value if the compiled code is an expression, not a series of statements. Your second usage is the correct one in this case.

If the code was simply '2 + 2' then Execute<int> would probably work, but I'm unable to check that at the moment.

answered Nov 29, 2011 at 16:48

Jeff Hardy

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