Just hailed like hell here, thought a window was going to break ;o)

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The latest drop of base4

Well, I've started working with the latest drop of Base4.net (version 2.1) - in fact I've decided to take the plunge and actually start using it for the project I'm currently working on (a work project, rather then a home project) so I should be giving it a pretty good thrashing over the next 3-6 months.  I already had a rough schema in place, so I generated types from it using the bundled web admin... It seems pretty cool... though I've struck a few things:

  • nvarchar(256) fields seems to show up as being 512 characters in length within base4.net...  I'm not sure if this is a bug with the schema interrogation, guess we'll find out as a I dig further in ;o) - though it's only skin deep of course, as you can change them to 256 with a quick edit.

  • I managed to create an assembly that was invalid... not sure how ;o) I could look at in reflector .Net, but base4 wasn't having a bar of it (even though it had generated it) - I must have screwed up a relationship somewhere, but I wasn't really sure... ended up just dumping it and starting from scratch again.

  • It doesn't seem that easy to refactor existing schema's using the web designer... while I was learning it would have been good to generate a schema, play with the assembly, then start editing and generate again... instead I ended up having to save the schema to disk, delete, edit, and recreate.  Still, it's pretty slick :)

I think though it probably all comes down to:
  • My urge to make things happen without understanding the in's and outs of base4.net
  • Horses for courses, the web admin is great for getting off to ground with base4.net, but I think I'll have to get down and dirty with the xml pretty soon...

Though I can't discuss the project, I can discuss what I'll be building it in... so we have:
  • Base4.Net
  • SQL 2005
  • Castle (Monorail & IoC)
  • NLog (or log4net... though I'm loosing faith in the latter)
  • NUnit
  • RhinoMocks
  • Splicer.Net
  • Some COM & Unmanaged code for audio processing

This is also the first time I've used monorail for a commercial project (we already use a lot of the facilities and the windsor container in the Syzmk RMP product) so it's certainly some interesting times... as we progress I'll give some feedback on both the Monorail and Base4.Net "user experience" :)
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Sourcode for "Integrating NUnit & IronPython"

Back again!

Here is the source for the last post: ironpython-and-nunit.zip (23.01 KB) - it's pretty rough around the edges (and in the middle :P) because I was just trying to see if it was possible, rather then to produce some production-level toolkit for integrating IronPython and NUnit.

Edit 2008-03-14: An updated version of the code target
NUnit 2.4 and VS2008 can be found here.


First off... usage is pretty straightforward.
  • Test fixtures must have NUnitFixture as one of their base classes.
  • Test methods must be prefixed with "test".
  • The setup method, if you need one, must be called "setUp"
  • The teardown method, if you need one, must be called "tearDown"
  • Fixture setup and teardown methods are also supported, they are called "setUpFixture" and "tearDownFixture".
  • Assert.XXX methods are the same as NUnit, unless you want to assert an exception is thrown.
  • For asserting an exception is thrown, make a call to "self.failUnlessRaises(...)" - it has the same syntax as the PyUnit equivalent, however it's tweaked slightly so it will work with Python exceptions, or CLR exceptions.
  • Do not perform an "Import * from System" in your test fixtures - it will clober the native Python Exception type, and may give you odd behaviour.


There are 8 classes and one python script which make up the implementation, the 8 classes are split between the "model"
(basically the python-side of the equation and the "NUnit extension" which are the necessary extensions to expose the model to NUnit...) - let's run through it quickly:

First we have the AbstractPythonSuite which hosts the python engine, and handles configuring and running the scripts containing the test fixtures.  Then we have a couple of classes which form the "model" consisting of a PythonFixture, representing a fixture, and PythonTestCase, representing a single test method in the fixture.

To build the model we have a PythonFixtureBuilder which is passed the python engine (from within the AbstractPythonSuite) and spits out all the fixture models, with the test cases assigned... this also assigns the various delegates for the setup/teardown/setupFixture/teardownFixture methods.

At this point the model is complete, it's just a matter of integrating it with NUnit - for this we have some more classes.

First of we need the PythonSuiteExtension, which represents the overall test suite, this contains PythonFixtureExtension's, for the fixtures, and finally PythonTestMethod for the individual test methods - the python extensions take care of running the tests in the model and calling the setup and tear down methods at the right times, and recording the results of course.

Last of all we have the PythonSuiteExtensionBuilder as mentioned in the last post, which takes care of creating the PythonSuiteExtension's for each class derived from AbstractPythonSuite it discovers in the target assembly.

Last of all we have a small python script which provides the necessary implementation for the base NUnitFixture class that all test fixtures are derived from... and a helper method we use in the PythonFixtureBuilder to identify the test methods in a class.

class NUnitFixture:
def __init__(self):
def setUp(self):
def tearDown(self):
def setUpFixture(self):
def tearDownFixture(self):
def failUnlessRaises(self, excClass, callableObj, *args, **kwargs):
if issubclass(excClass, System.Exception):
callableObj(*args, **kwargs)

except Exception, e:

if hasattr(e, "clsException") and
(type(e.clsException) == excClass):
callableObj(*args, **kwargs)
except excClass:
if hasattr(excClass,'__name__'):
excName = excClass.__name__

excName = str(excClass)

raise AssertionException("%s not raised" % excName)

def getTestCaseNames(testCaseClass, prefix):
def isTestMethod(attrname, testCaseClass=testCaseClass, prefix=prefix):
return attrname.startswith(prefix) and callable(getattr(testCaseClass, attrname))
testFnNames = filter(isTestMethod, dir(testCaseClass))
for baseclass in testCaseClass.__bases__:
for testFnName in getTestCaseNames(baseclass, prefix):
if testFnName not in testFnNames:
return testFnNames

And that's all there is to it...  If anyone actually finds this useful and wants to build on from it, please feel free, and if at all possible keep it open source (though you don't have to...)

Something to keep in mind is that at the moment if your test fixture can't actually be parsed and executed by the python engine, that exception will bubble up, eventually stopping the test assembly from being loaded at all... I think the nicer solution to this would be to add a custom NUnit test case for each script that failed to load, which in turn fails when executed as part of the assembly - dumping out the exception raised during construction.

At least then a tool like TestDriven.Net would quickly notify the developer of their mistake, instead of just falling over.

And very last of all, though I've been manually specifying the names of the script files.. using a class declaration like this:

public class MyPythonSuite : AbstractPythonSuite
public MyPythonSuite()
: base("MyPythonFixture.py")

You could make it a little more dynamic and do something like this:

public class DynamicPythonSuite : AbstractPythonSuite
public DynamicPythonSuite()
: base(FindSuitablePythonScripts())

private static string[] FindSuitablePythonScripts()
List scripts = new List();
Assembly assembly = typeof (DynamicPythonSuite).Assembly;
string indication = "#test";
foreach (string potentialScript in assembly.GetManifestResourceNames())
using (StreamReader reader =
new StreamReader(assembly.GetManifestResourceStream(potentialScript)))
if (reader.ReadLine().Trim().StartsWith(indication,
true, CultureInfo.InvariantCulture))
return scripts.ToArray();

Which will load all scripts with "#test" in the first line, which seem'is a little easier to me (not having to spell out the path to the script, and only having to create the test file to make things happen) - YMMV of course.
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Integrating NUnit & IronPython...

Breaking scripts

I've been thinking about the issues involved with using
IronPython in a product as a scripting language, internally we've
already struggled at Syzmk with my love of refactoring breaking
scripts in our deployed products left right and centre.

I think the problems I need to solve first are:

  • Ensuring an understanding of the user experience when
    scripting with the application (read: dogfooding the scripting

  • Making sure I identify where helper classes / wrappers etc.
    may be necessary to make the scripting experience more palatable
    to end users.
  • Ensuring any changes don't clobber the contracts between the
    scripting language and the client when refactoring the underlying
    .Net classes they rely on.

Regression tests for expected script usage is what it comes
down... but if you sit down and start trying to write these tests
in NUnit it all gets a bit unwieldy - there's a lot of time
wasted making sure your tabs are right, escaping characters
correctly in strings, and running scripts, evaluating the
results, and then asserting against them - it's frustrating, and
fails to emulate the experience of your users who are writing
scripts purely in Python.


So my next port of call was to try the unit testing support that
comes with python (PyUnit) - it would definitely do the job - but
then I need to do a couple of things... first I need to start
bundling quite a few standard libraries with the scripting engine
in our product, and then I have to write additional functionality
to support capturing the results of running the PyUnit tests and
presenting them to the automated build process... It's all
sounding like a pain in the ass, and  the automation build
works nicely as it is, I'd rather not have to mess with it...

So I decided to do a little integration work, to see if I could
run a test suite written in python as part of a C# assembly.

NUnit meets (Iron)Python

First off, my solutions user experience is ok - not perfect - but
then I just wanted to make sure I could get it working, before I
put any effort into cleaning it up, and not being an expert in
extending NUnit, or coding python, it was probably doomed from
the start to be a mediocre solution ;o)

The steps to get it working in a test assembly are:

  1. Writing a fixture in python, and including it in the assembly
    as an embedded resource.
  2. Creating a suite which references the embedded python files -
    this is a class derived from the "AbstractPythonSuite".

  3. Creating a Suite builder (I had to do this in the test
    assembly itself, because it wasn't working when I bundled this in
    a support library).
  4. Run the suite ;o)

First off, we write the fixture, the only requirements are:

  • The fixture class is derived from "NUnitFixture".
  • The test methods are prefixed with "test" - as per PyUnit.
    And take only a "self" argument.

Here's an example fixture:

import System
from System import Console

class MyPythonFixture(NUnitFixture):

def testPass(self):

def testFail(self):
Assert.IsTrue(False, "this will fail")

As you can see we are just using the existing NUnit Assert
methods... There is one caveat to this that I will cover in
another post (that of testing for expected exceptions).

Next we create a suite - which can wrap one or more python script
files (included as assembly resources) - this is all we need to
bridge the gap.

public class MyPythonSuite : AbstractPythonSuite
public MyPythonSuite()
: base("MyPythonFixture.py")

And last of all, we need to drop in a suite builder - in theory I
should be able to include this in a support assembly - but it
doesn't seem to work, here's the code:

public class PythonSuiteExtensionBuilder : ISuiteBuilder
public TestSuite BuildFrom(Type type, int assemblyKey)
if (CanBuildFrom(type)) return new PythonSuiteExtension(type, assemblyKey);
return null;

public bool CanBuildFrom(Type type)
return (typeof(AbstractPythonSuite).IsAssignableFrom(type) && (type != typeof(AbstractPythonSuite)));

At this point when can test the assembly with NUnitGui,
and see our python fixtures appear under the "MyPythonSuite"...
pretty slick huh?

border="0" />

The big downsides of this approach are that you can't run the
tests individually using something like TestDriven.Net,
and Resharper's unit test window doesn't pick them up...
However NUnitGui and the corresponding NUnitConsole
have no problems with them, and running all the tests in your
assembly with TestDriven.Net does pick them up thankfully
- so as long you don't have many slow tests in your assembly it
should still be tolerable (you can run them while still

And of course, they will be picked up in your automated builds -
which is great news for me... I hate messing around with
CruiseControl.Net's configuration.

I'll tidy up the implementation a little and post the code

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help() works...

Well, Seo Sanghyeon asked me a pretty reasonable question of the last entry

"Why don't you use help(), instead of printing Overloads?"

Good question, I didn't realise that actually worked in IronPython for .Net types, I was very pleasantly surprised, I remember in the early betas i tried using help() on various managed types and it would just raise a NotImplementedException exception (or something like that, I forget now) - so what does that mean for my examples... well... let's take a system type like Guid and use help() on it.

IronPython 1.0.60816 on .NET 2.0.50727.42
Copyright (c) Microsoft Corporation. All rights reserved.

>>> import System

>>> from System import *

>>> help(Guid)

Help on Guid in module System in mscorlib, Version=,
Culture=neutral, PublicKeyToken=b77a5c561934e089

 |      Guid(Array[Byte] b)

 |      Guid(UInt32 a, UInt16 b,
UInt16 c, Byte d, Byte e, Byte f, Byte g, Byteh, Byte i, Byte j,
Byte k)

 |      Guid(str g)

 |      Guid(int a, Int16 b, Int16
c, Array[Byte] d)

 |      Guid(int a, Int16 b, Int16
c, Byte d, Byte e, Byte f, Byte g, Byte h, Byte i, Byte j, Byte

 |      Guid


 |  Data and other attributes defined here:


 |      CompareTo(...)

int CompareTo(self, object value)

int CompareTo(self, Guid value)

 |      Equals(...)

bool Equals(self, object o)

bool Equals(self, Guid g)

 |      Finalize(...)


 |      GetHashCode(...)

int GetHashCode(self)

 |      GetType(...)

Type GetType(self)

 |      MemberwiseClone(...)

object MemberwiseClone(self)

 |      NewGuid(...)

Guid NewGuid()

 |      ToByteArray(...)

Array[Byte] ToByteArray(self)

 |      ToString(...)

str ToString(self)

str ToString(self, str format)

str ToString(self, str format, IFormatProvider provider)

 |      __eq__(...)

bool op_Equality(Guid a, Guid b)

 |      __init__(...)

x.__init__(...) initializes x; see x.__class__.__doc__ for

x.__init__(...) initializes x; see x.__class__.__doc__ for

 |      __ne__(...)

bool op_Inequality(Guid a, Guid b)

 |      __new__(...)

__new__(cls, Array[Byte] b)

__new__(cls, UInt32 a, UInt16 b, UInt16 c, Byte d, Byte e, Bytef,
Byte g, Byte h, Byte i, Byte j, Byte k)

__new__(cls, str g)

__new__(cls, int a, Int16 b, Int16 c, Array[Byte] d)

__new__(cls, int a, Int16 b, Int16 c, Byte d, Byte e, Byte f,
Byte g, Byte h, Byte i, Byte j, Byte k)

Guid CreateInstance[Guid]()



Sweet, it works a treat - and will save a lot of digging time - though you might want to capture the results for big classes ;o)

Thanks Seo!

(btw, Seo is the man behind the Iron Python Community Edition & FePy projects - which can be found on sourceforge) and I would have to agree with this article that he does seem almost OmniPresent in the IronPython community...

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