Python – Script arguments and Embedded IronPython

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I have an embedded scripting engine in my C# application that uses IronPython 2. I create the Python runtime and add a few classes to the global namespace so that the script can import them as modules.

However, one (pretty basic) thing I can't figure out is how to send script arguments. I realize that I could just create a variable with a list of arguments, but there must be a proper way to do it. Also, doing it in the proper 'Python' way allows me to compile the scripts and use an automated document builder called Sphinx. So the ultimate goal is to be able to use:

import sys
sys.argv

In one of my scripts and have it get the arguments the user specified (through the C# app).

Right now, I call the script by using:

// set up iron python runtime engine
_engine = Python.CreateEngine();
_runtime = _engine.Runtime;
_scope = _engine.CreateScope();

// run script
_script = _engine.CreateScriptSourceFromFile(_path);
_script.Execute(_scope);

And I've tried searching for an API to add script arguments with no luck. I've also tried appending them to the script path (_path in example) with no luck. I tried with CreateScriptSourceFrom File and CreateScriptSourceFromSting (which was a long shot anyway…).

Is what I'm trying to do even possible?

Best Answer

When you create the engine, you can add an "Arguments" option the contains your arguments:

IDictionary<string, object> options = new Dictionary<string, object>();
options["Arguments"] = new [] { "foo", "bar" };
_engine = Python.CreateEngine(options);

Now sys.argv will contain ["foo", "bar"].

You can set options["Arguments"] to anything that implements ICollection<string>.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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