IronPython integration in C#: a specific problem/question

Question

I'm working on providing an extensibility mechanism for my C# mapmaking application through IronPython. Everything works fine, but I have a specific requirement which I'm having trouble implementing: I want the user to be able to specify two things:

A file name of the Python script to be loaded
A one-liner string containing Python script which would typically be a call of a function from that Python file (example getTextLabel(element))

These two settings must be separate, but I don't know if it is possible to do this using PythonScript and related classes.

I'm a newbie in Python, perhaps there is another way to achieve this? For performance reasons I want to avoid loading and compiling the Python script file several times (since there could be several above mentioned different "function call" settings and I want to reuse the CompiledCode instance for the file if possible).

UPDATE: @digEmAll gave the correct answer to my question, so I'm accepting it as a valid answer. But if you are concerned with performance, you should also check out my own answer.

digEmAll · Accepted Answer · 2011-03-13 22:11:54Z

5

You can do something like this:

string importScript = "import sys" + Environment.NewLine +
                      "sys.path.append( r\"{0}\" )" + Environment.NewLine +
                      "from {1} import *";

// python script to load
string fullPath = @"c:\path\mymodule.py";

var engine = Python.CreateEngine();
ScriptScope scope = engine.CreateScope();

// import the module
string scriptStr = string.Format(importScript,
                                 Path.GetDirectoryName(fullPath),
                                 Path.GetFileNameWithoutExtension(fullPath));
var importSrc = engine.CreateScriptSourceFromString(scriptStr,Microsoft.Scripting.SourceCodeKind.File);
importSrc.Execute(scope);

// now you ca execute one-line expressions on the scope e.g.
string expr = "functionOfMyModule()";
var result = engine.Execute(expr, scope);

As long as you keep the scope where the module is loaded, you can call functions of the module without reloading it.

edited Mar 13, 2011 at 22:11

answered Mar 13, 2011 at 22:05

digEmAll

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3 Comments

Igor Brejc Over a year ago

Thanks, I'll do some testing and if this works OK, I'll accept your answer. BTW is there a way to clone the scope? For example to avoid one function call to affect the execution of subsequent function calls?

digEmAll Over a year ago

Mmh, I don't think it's possible... and if it was, it wouldn't be much faster than create a new scope and re-load the desired modules...

Igor Brejc Over a year ago

your code runs, thanks for your help. Also check out my own answer.

Igor Brejc · Accepted Answer · 2011-03-14 18:04:11Z

5

I've done some testing of @digEmAll's code. First I must say it runs correctly and does what I asked in the question. But I was concerned with the fact that you have to call

string expr = "functionOfMyModule()";
var result = engine.Execute(expr, scope);

every time you want to evaluate a user-defined expression. My concern was that the code is not pre-compiled and has to be reparsed on each execution, which could have a serious effect on the performance of my application (these kinds of expressions could be called hundreds of thousands if not millions of times, so every millisecond counts).

I tried a different solution: simply pasting the user-defined expression at the end of the Python module (I'm not saying this works in all situations!):

def simpleFunc(x):
    return x + 2;

# this is where the pasting occurs:
simpleFunc(x)

What I did then is to compile this code:

 ScriptSource source = engine.CreateScriptSourceFromString(myCode);
 CompiledCode compiledCode = source.Compile();

... create a scope and run it:

 ScriptScope scope = engine.CreateScope();
 scope.SetVariable ("x", 10);
 int result = compiledCode.Execute<int>(scope);

Now I executed both solutions (digEmAll's and my own) on the same piece of code and the same expression 10,000 times and here are the results:

engine.Execute(expr, scope): 0.29 ms / run
compiledCode.Execute(scope): 0.01 ms / run

So I guess I'll try to use my own solution, unless the code pasting proves to be a problem.

answered Mar 14, 2011 at 18:04

Igor Brejc

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2 Comments

digEmAll Over a year ago

Yes, that's perfectly working too. Of course compiling the code (and saving a call to Execute) it's faster, I didn't think to it ;)

sll Over a year ago

Guys, what if on C# side you do not know parameter/variable names and want to substitute parameters by a real values, like A if B > C else D so given expression how would you replace such parameters A,B,C,D by the real numbers? I've only such expression string. Thanks in advance

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