Beginning IronPython

Introduction

Okay, so you’ve read the chapter on IronPython syntax. Brilliant, learning a new programming language is easy! You feel like such a polyglot. What’s all the fuss about?  All that remains now is a few formalities. Install the framework and knock out a quick app to demonstrate how easy it is. The only problem is that nothing works and the error messages make no sense.

Back to the world of the programming beginner.

You need to learn a few practical lessons before you can say that you are a competent Python programmer. It is important to be able to interpret the common error messages and structure your project.  Normally you will find that the official documents will gloss over this stuff because they like to leave it to your discretion. As a result you will find yourself searching the internet for a blog to help!

• You can execute from the command line with ipy.exe, use the IronPython Console or the VS Tools.

Example, calling C# code from IronPython

Use IronPython to create some tests/specifications; one static .NET CLR class and one normal .NET CLR class. The classes will be contained in an assembly project called Polyglot, as we want to use multiple programming languages in this example.

• Greet static class. This will have one method and one property. The method accepts a parameter, a name, and the returns a greeting for that name, e.g. “Hello Jon”. The property simply returns a string “Hello World!”.
• Math class. This class deals with simple arithmetic, does not handle negative numbers maintains a list of answers. It has Add and Subtract methods and the Subtract method throws an exception if it cannot return a positive number. It also has an array containing all the results with the most recent result at the beginning of the list.

RunTests.py 

  1  import sys
  2  import unittest
  3  import clr
  4  sys.path.Add('C:\\sut') # folder containing software to be tested
  5  clr.AddReferenceToFile('Polyglot.dll')
  6  
  7  from Polyglot import Greet
  8  
  9  class GreetTest(unittest.TestCase):
 10      softwareUnderTest = Greet
 11      def testGreet_ShowCsGreeting_GreetWithName(self):     
 12          self.assertEquals('Hello Brian', self.softwareUnderTest.GreetMe('Brian'), 'Greet Me test')        
 13      def testGreet_ShowCsGreeting_GreetHello(self):  
 14          self.assertEquals('Hello World!', self.softwareUnderTest.Hello, 'Greet Hello test')
 15  
 16  from Polyglot import Math
 17  
 18  class MathTest(unittest.TestCase):
 19      softwareUnderTest = Math()
 20      def testMath_Add_Simple(self):
 21          self.assertEquals(3, self.softwareUnderTest.Add(1,2), 'Simple Add')
 22      def testMath_Subtract_Simple(self):
 23          self.assertEqual(3, self.softwareUnderTest.Subtract(5,2), 'Simple Subtract')
 24      def testMath_Subtract_NegativeResultFails(self):
 25          with self.assertRaises(ValueError):
 26              self.softwareUnderTest.Subtract(3, 4)
 27      def testMath_Results_IsSetAndOrdered(self):
 28          result1 = 2
 29          result2 = 3
 30          result3 = 4
 31          self.softwareUnderTest = Math()
 32          self.assertEqual(0, len(self.softwareUnderTest.Results)) # to begin with there are no results
 33          self.softwareUnderTest.Add(1,1)
 34          self.assertEqual(1, len(self.softwareUnderTest.Results)) # after one operation there will be one result
 35          self.assertEqual(result1, self.softwareUnderTest.Results[0]) # check the result
 36  
 37          # run a couple more operations and check they are stored propery
 38          self.softwareUnderTest.Subtract(5,2)
 39          self.softwareUnderTest.Add(2,2)
 40          self.assertEqual(result3, self.softwareUnderTest.Results[0])
 41          self.assertEqual(result2, self.softwareUnderTest.Results[1])
 42          self.assertEqual(result1, self.softwareUnderTest.Results[2])
 43  
 44  try:
 45      if __name__ == '__main__':
 46          unittest.main()
 47  except:
 48      e = sys.exc_info()[0]
 49      print( "Error: %s" % e )
 50      clr.ClearProfilerData() # unload the .dll file so the file lock is released
 51  
 52  a=raw_input('The end!')  

copy $(TargetPath) C:\sut
copy $(TargetDir)$(TargetName).pdb C:\sut

namespace Polyglot
{
    public static class Greet
    {
        public static string GreetMe(string name)
        {
            return string.Format("Hello {0}", name);
        }

        public static string Hello { get { return "Hello World!"; } }
    }
}

using System.Collections.Generic;

namespace Polyglot
{
    public class Math
    {
        List _results;
        public Math()
        {
            _results = new List();
        }

        public uint Add(uint x, uint y)
        {
            return lastResult = x + y;
        }

        public uint Subtract(uint x, uint y)
        {
            if (y > x)
                throw new System.ArgumentException("Operation would result in a negative result");

            return lastResult = x - y;
        }

        private uint lastResult
        {
            set
            {
                _results.Insert(0, value);
            }
        }

        public uint[] Results
        {
            get { return _results.ToArray(); }
        }
    }
}