Using Python Expressions from C# Code

Utilizing the dynamic features of C# and the Dynamic Language Runtime (DLR), among other things, allows C# programs to interoperate with other dynamic languages built on top of the DLR.

For example, Python has the ability to chain operators, for example the expression “10 < 15 < 20” returns true: 10 is less than 15 and 15 is less than 20.

To use a chained Python expression from C# code, IronPython can be used.

To get started (in this example a C# console application) first install the IronPython NuGet package. This allows the application to interoperate with Python code.

The following code shows a console application that evaluates a user-entered number “n” against the Python expression “10 < n < 20”:

using IronPython.Hosting;
using Microsoft.Scripting;
using Microsoft.Scripting.Hosting;
using static System.Console;

namespace PythonCSharp
    class Program
        static void Main(string[] args)
            const string pythonExpression = "10 < n < 20";

            int n;

            while (true)
                WriteLine($"Enter a value for n where {pythonExpression}");

                n = int.Parse(ReadLine()); // cast error check omitted

                ScriptEngine pythonEngine = Python.CreateEngine();

                ScriptScope pythonScope = pythonEngine.CreateScope();

                // set the value of the Python token "n" in the expression 10 < n < 20
                pythonScope.SetVariable("n", n);

                ScriptSource pythonScriptSource = pythonEngine.CreateScriptSourceFromString(pythonExpression, SourceCodeKind.Expression);

                // Execute the Python expression and get the return value
                dynamic dynamicResult = pythonScriptSource.Execute(pythonScope);

                WriteLine($"{pythonScriptSource.GetCode().Replace("n", n.ToString())} = {dynamicResult}");


Running the console application allows the user to enter a value for “n” and evaluate it against the Python expression as the following image shows:

Console application calling Python Expression from CSharp

To learn more about how C# makes dynamic possible, some potential use cases, and more detailed on implementing custom types check out my Dynamic C# Fundamentals Pluralsight course.

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