I am trying to use IronPython as an external scripting language for Unity3D. The necessary DLLs for IronPython's execution load just fine inside of Assets\Plugins. However, when I try to run the script I get this error:

PythonImportErrorException: No module named UnityEngine
IronPython.Modules.Builtin.__import__ (IronPython.Runtime.Calls.ICallerContext,string,object,object,object) <IL 0x0003b, 0x001cc>
(wrapper dynamic-method) object.__import__##5 (IronPython.Runtime.Calls.ICallerContext,object,object,object,object) <IL 0x0000e, 0x0004d>
IronPython.Runtime.Calls.FastCallableWithContextAny.Call (IronPython.Runtime.Calls.ICallerContext,object,object,object,object) <IL 0x00015, 0x00067>
IronPython.Runtime.Calls.BuiltinFunction.Call (IronPython.Runtime.Calls.ICallerContext,object,object,object,object) <IL 0x0000d, 0x00058>
IronPython.Runtime.Operations.Ops.CallWithContext (IronPython.Runtime.Calls.ICallerContext,object,object,object,object,object) <IL 0x00012, 0x000b0>
IronPython.Runtime.Importer.Import (IronPython.Runtime.PythonModule,string,IronPython.Runtime.List) <IL 0x0000d, 0x0006c>
IronPython.Runtime.Operations.Ops.Import (IronPython.Runtime.PythonModule,string) <IL 0x00007, 0x0003b>
(wrapper dynamic-method) object.<string>##1 (IronPython.Runtime.ModuleScope) <IL 0x0006b, 0x00210>

The script and the 'UnityEngine.dll' are located in the same folder. This is the script:

import clr
clr.LoadAssemblyFromFile("UnityEngine.dll")

import UnityEngine
from UnityEngine import *

Debug.Log("Hello World from Python!")

So from a Unity script:

PythonEngine engine = new PythonEngine();
engine.LoadAssembly(Assembly.GetAssembly(typeof(GameObject)));
engine.ExecuteFile("apple.py");

And inside of a python script (mine was apple.py located in the same folder as the game.exe):

import UnityEngine
from UnityEngine import *

Debug.Log("Hello From IronPython!")

Edit #1

I should note that the reason I was getting an error before was because the runtime version was specified as a 4.0 instead of a 3.5 or lower.

Edit #2

If you need to access your scripts from IronPython, then you can load your assembly as well by doing:

engine.LoadAssembly(Assembly.GetAssembly(typeof(MyPlayerScriptOrSomething)));

Then to use it in script:

import MyPlayerScriptOrSomething

Note that you do not have to do the LoadAssembly for every script, just once to get the assembly.

Edit #3

The IronPython DLLs should be placed in a "Plugins" folder somewhere under "Assets" (most simply: Assets->Plugins. Here is my setup:

> Assets
> > Plugins
> > > IronMath.dll
> > > IronPython.dll
> > > Microsoft.Scripting.dll
> > > Microsoft.Scripting.Core.dll

Edit #4

Your scripts can be put anywhere your program has access to them. For instance, if you wanted to place "apple.py" directly under "C:\", you could execute that file by doing: