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PythonNET: C# function does not modify class instanced passed to it

I have a C# class like
public MY_CLASS(int number)
{
SomeField = number;
SetElseWhere = 0;
}
}
that I want to pass to a C# function like
public static bool MyTask(string pathXML, out MY_CLASS test)
I expect MyTask to modify the field SetElseWhere in an instance of MY_CLASS
In PythonNet I call the function like
import System
my_dll = System.Reflection.Assembly.LoadFile('example.dll')
MY_CLASS_t = my_dll.GetType('NAMESPACE.MY_CLASS')
my_instance = System.Activator.CreateInstance(MY_CLASS_t)
x = MyTask('test.xml', my_instance)
Now it is getting strange, at least to me:
The returned value x is a tuple with two entries, a boolan and an object
of type NAMESPACE.MY_CLASS. But it is not the instance that I sent in as second parameter stated with property out.
When I check the results I can see that the object in the returned
tuple has been modified correctly, but the instance I send in
has not been modified.
Any ideas why?

Ok, I finally understood your problem and this issue is not documented. There is no concept of out/ref arguments in Python, hence the modifications to arguments are returned in the tuple.
Here is an open issue about this:
https://github.com/pythonnet/pythonnet/issues/228

Can not implicity convert type Systems.Collection.Generic.List<feedEventViewModel> to Proj.Areas.Management.Models.FeedEventViewModel

I'm trying to convert a view model to list and then return it to the view but am getting the cannot implicity convert type error.
Code:
public ActionResult Index(FeedEventCommand command)
{
var feedEventViewModel = new FeedEventViewModel
{
AnimalId = command.AnimalId,
AnimalName = command.AnimalName,
FeederTypeId = command.FeederTypeId,
FeederType = command.FeederType
};
feedEventViewModel = new List<feedEventViewModel>(); <--Error line
return View(feedEventViewModel);
}
What am I doing wrong in this case?

feedEventViewModel is already declared as a single object, you can't declare it again as a List<FeedEventViewModel>(). Other language such as Rust allows you to "shadow" the variable declaration but C# not (and var is just a shorter way to declare a variable).
You can solve this issue quite easily:
return View( new List<FeedEventViewModel>() {
new FeedEventViewModel{
AnimalId = command.AnimalId,
AnimalName = command.AnimalName,
FeederTypeId = command.FeederTypeId,
FeederType = command.FeederType
}
}
);

You may be misunderstanding what the var keyword is doing here. When you declare a variable with var you are not saying that the variable can be anything, you are saying to the compiler that it can work out what the type is without you needing to specify it precisely.
So in your example (or a slight modification) when the compiler encounters the code:
var feedEventViewModel = new FeedEventViewModel();
it will see that the right hand side of the assignment is of type FeedEventViewModel and so the variable feedEventViewModel will be of that type. In effect it will be like you typed:
FeedEventViewModel feedEventViewModel = new FeedEventViewModel();
Any later use of that variable must be in line with this declaration so when you do feedEventViewModel = new List<feedEventViewModel>(); the compiler rightly says that List<feedEventViewModel> is not of the type expected by feedEventViewModel. There is such a thing as implicit conversions whereby the compiler knows how to convert between two different types and is allowed to do it without it being specifically requested but no such implicit conversions were found, hence the error.
It is unclear from the information given what exactly you are doing (is the item you created meant to be on the list? Does your view expect a list or a single item?). If you need a list with the item in then I'd just go with:
var list = new List<feedEventViewModel>(){feedEventViewModel };
return View(list);

C# list in function param

I'm new to C#. I want to take a list as argument and return another from the data I get from the first one.
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = new List<DestinationGenericMapProps>(datas);
return result;
}
I get this error:
Error 241 The best overloaded method match for System.Collections.Generic.List<VDDataUpdaterGeneric.DataObjects.DestinationGenericMapProps>.List(int) has some invalid arguments
I know this is probably pretty basic but I'm new to C# and struggle with this. Thanks for your help.

List<BoutiqueInWebService> is not a List<DestinationGenericMapProps>.
This will not work unless BoutiqueInWebService is derived from DestinationGenericMapProps.
Basically, there is a List<T>(IEnumerable<T>) constructor, but the T's have to be the same.
Either change your return type to List<BoutiqueInWebService> and change your new statement:
private List<BoutiqueInWebService> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = new List<BoutiqueInWebService>(datas);
return result;
}
or change your parameter to be of type List<DestinationGenericMapProps>:
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<DestinationGenericMapProps> datas)
{
var result = new List<DestinationGenericMapProps>(datas);
return result;
}
Alternatively, if you know how to make a DestinationGenericMapProps from a BoutiqueInWebService, you can use System.Linq and perform a select against the argument:
private List<DestinationGenericMapProps> ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
var result = datas.Select(x => new DestinationGenericMapProps() { ... }).ToList();
return result;
}

Your method return type is a list of DestinationGenericMapProps, but you're trying to create list of BoutiqueInWebService (which is data).
You can do this to match your return type:
private List<DestinationGenericMapProps>
ConstructDestinationMapPropsList(List<BoutiqueInWebService> datas)
{
return (from d in datas
select new DestinationGenericMapProps()
{
// map properties here
Prop1 = d.SomePropInData
}).ToList();
}

You're getting the error because you're trying to populate a list of one type (DestinationGenericMapProps) with objects from a list of a different type (BoutiqueInWebService) which isn't type safe.
You can only do this if BoutiqueInWebService inherits from DestinationGenericMapProps.

C# supports function overloading, which means that a class can have more than one function with the same name as long as the parameters are different. The compiler decides which overload to call by compairing the types of the parameters. This applies to constructors too.
The List class has a three overloads of its constuctor:
List<T>()
List<T>(IEnumerable<T>)
List<T>(int)
I assume that you are trying to use the second of those as it will create a new list from the passed in one. For the list you are creating T is a DestinationGenericMapProps. So the constructors are:
List<DestinationGenericMapProps>()
List<DestinationGenericMapProps>(IEnumerable<DestinationGenericMapProps>)
List<DestinationGenericMapProps>(int)
The list you have passed in has T set to BoutiqueInWebService. As such the compiler is trying to find a constructor like this in the list above.
List<DestinationGenericMapProps>(IEnumerable<BoutiqueInWebService>)
As it can't find one it raises the error you have recieved.
Is it possible to cast a BoutiqueInWebService to a DestinationGenericMapProps object? If so you could do this:
var result = datas.Cast<DestinationGenericMapProps>().ToList()
If no direct cast is possible it may be possible to do a long hand cast like this:
var result = datas.Select(o => new DestinationGenericMapProps() { PropA = o.PropA, PropB = o.PropB /* etc */}).ToList();

Call function in dynamic linq

I'm trying to call a function in a dynamic linq select statement, but im getting error:
No property or field 'A' exists in type 'Tuple2'
Example code:
void Main()
{
var a = new Tuple<int, int>(1,1);
var b = new[]{ a };
var q = b.AsQueryable().Select("A.Test(it.Item1)");
q.Dump();
}
public static class A
{
public static int Test(int i)
{
return i++;
}
}
How should I change my code to get this working?
If I call built in function Convert.ToInt32 for example it works fine.
var q = b.AsQueryable().Select("Convert.ToInt32(it.Item1)");
Also how do I cast a property using dynamic linq?
var q = b.AsQueryable().Select("((float)it.Item1)");

I'll say that the dynamic-linq isn't "strong enough" to do these things. It looks for methods only in the given objects and some special classes: Math, Convert, the various base types (int, float, string, ...), Guid, Timespan, DateTime
The list of these types is clearly visible if you use ilspy/reflector on the file. They are in System.Linq.Dynamic.ExpressionParser.predefinedTypes .
Now, clearly I could be wrong, but this works: .Select("Guid.NewGuid().ToString()").Cast<string>().ToArray()
showing that it's quite probable that that is the "correct" list.
There is an article here on how to modify Dynamic LINQ if you are interested http://www.krizzcode.com/2012/01/extending-dynamiclinq-language.html
Now, an intelligent man would take the source of dynamic linq and simply expand that array... But here there aren't intelligent men... There are only programmers that want blood! Blood but especially innards!
var type = typeof(DynamicQueryable).Assembly.GetType("System.Linq.Dynamic.ExpressionParser");
FieldInfo field = type.GetField("predefinedTypes", BindingFlags.Static | BindingFlags.NonPublic);
Type[] predefinedTypes = (Type[])field.GetValue(null);
Array.Resize(ref predefinedTypes, predefinedTypes.Length + 1);
predefinedTypes[predefinedTypes.Length - 1] = typeof(A); // Your type
field.SetValue(null, predefinedTypes);
Do this (with the types you want) BEFORE the first call to Dynamic Linq (because after the first call the methods/properties of these types are cached)
Explanation: we use reflection to add our object(s) to this "special list".

I know there is already an accepted answer on this but it did not work for me. I am using Dynamic Linq 1.1.4. I wanted to do a query like this
$.GetNewestRisk() == null
Where GetNewestRisk() is a public method on the object represented by $. I kept getting this error "Error running query, Methods on type 'Patient' are not accessible (at index 2)".
I found in the source code there is a GlobalConfig object that allows a custom provider to be assigned which will hold all of the types you may want to work with. Here is the source code for the custom provider:
public class CustomTypeProvider: IDynamicLinkCustomTypeProvider
{
public HashSet<Type> GetCustomTypes()
{
HashSet<Type> types = new HashSet<Type>();
types.Add(typeof(Patient));
types.Add(typeof(RiskFactorResult));
types.Add(typeof(PatientLabResult));
types.Add(typeof(PatientVital));
return types;
}
}
Here is how I am using it:
System.Linq.Dynamic.GlobalConfig.CustomTypeProvider = new CustomType();
After making this call I am able to call methods on the objects inside of the expression.

#xanatos answer doesn't work for .Net Core version. So I've found something similar related by #Kent on the System.Dynamic.Linq.Core tests DynamicExpressionParserTests written by the library's author himself.
The given TestCustomTypeProviderClass allows you to use the DynamicLinqType class annotation which is pretty usefull for this problem.
To answer to question, you then just needed to defined the class (ensure to annotate with DynamicLinqType) :
[DynamicLinqType]
public static class A
{
public static int Test(int i)
{
return i++;
}
}
Add a customTypeProvider as mentioned above :
private class TestCustomTypeProvider : AbstractDynamicLinqCustomTypeProvider, IDynamicLinkCustomTypeProvider
{
private HashSet<Type> _customTypes;
public virtual HashSet<Type> GetCustomTypes()
{
if (_customTypes != null)
{
return _customTypes;
}
_customTypes = new HashSet<Type>(FindTypesMarkedWithDynamicLinqTypeAttribute(new[] { GetType().GetTypeInfo().Assembly }));
return _customTypes;
}
}
and use a ParsingConfig with the configurable Select to call it :
var config = new ParsingConfig
{
CustomTypeProvider = new TestCustomTypeProvider()
};
var q = b.AsQueryable().Select(config, "A.Test(it.Item1)");

#Armand has put together a brilliant solution for this issue, and being the only solution I was able to find regarding this I want to add to it for anyone who tries the same approach.
The class that is marked with...
[DynamicLinqType]
... must be taken into consideration when you run the following line:
FindTypesMarkedWithDynamicLinqTypeAttribute(new[] { GetType().GetTypeInfo().Assembly })
In the solution provided above, this assumes the class that contains the function to be evaluated is on the same class the code currently resides in. If the methods are to be used outside of said class, the assembly will need to change.
FindTypesMarkedWithDynamicLinqTypeAttribute(new[] { typeof(AnotherClassName).Assembly })
Nothing changes from the solution above, this is just for clarification for anyone attempting to use it.

As regards the current version (1.2.19) of Dynamic LINQ, you will probably get another exception:
System.Linq.Dynamic.Core.Exceptions.ParseException : Enum value 'Test' is not defined in enum type 'A'
To make DLINQ know your type 'A', you have two options:
Set up parsing config with your own custom types provider where you directly specify the type 'A'.
Mark your type with the attribute [DynamicLinqType]. If that type is loaded into the current domain (that's the usual case), you don't have to do anything more since the default custom type provider already scans the current AppDomain for types marked with [DynamicLinqType]. And only if that's not the case, i.e. your type is not loaded into the current domain, you have to do something like in that answer.
What if you would like to use both approaches - the first for type 'A' and the second for type 'B'? In that case, you just have to "merge" your type 'A' with the default provider types:
public class DynamicLinqTests
{
[Test]
public void Test()
{
var a = new Tuple<int, int>(1, 1);
var b = new[] { a };
var parsingConfig = new ParsingConfig
{
ResolveTypesBySimpleName = true,
CustomTypeProvider = new TestCustomTypesProvider()
};
var queryWithA = b.AsQueryable().Select(parsingConfig, "A.Test(it.Item1)");
queryWithA.ToDynamicList();
var queryWithB = b.AsQueryable().Select(parsingConfig, "B.Test(it.Item1)");
queryWithB.ToDynamicList();
}
public static class A
{
public static int Test(int i)
{
return i++;
}
}
[DynamicLinqType]
public static class B
{
public static int Test(int i)
{
return i++;
}
}
public class TestCustomTypesProvider : DefaultDynamicLinqCustomTypeProvider
{
public override HashSet<Type> GetCustomTypes()
{
var customTypes = base.GetCustomTypes();
customTypes.Add(typeof(A));
return customTypes;
}
}
}

I may be confused but your syntax whereby you are using a string in your Selects doesn't compile for me. The following syntax works:
var q = b.AsQueryable().Select(it => A.Test(it.Item1));

var b = new[]{ a };
The above array is don't know what type of array , and it's not type safe ?
Your values are assigned in variant data type so it's not integer value (I think string value) ,when you get this values in your query must need to convert.toint32() because your class parameter data type is integer
Please try it
var b = new **int**[]{ a };
instead of var b = new[]{ a };
The important hint is here (in bold):
No property or field 'xxx' exists in **type** 'xxx'
And Please look this for previous discussion :
Dynamic Linq - no property or field exists in type 'datarow'

The following works for me:
var a = new Tuple<int, int>(1, 1);
var b = new[] { a };
var q = b.AsQueryable().Select(it=>A.Test(it.Item1));
var q1 = b.AsQueryable().Select(it => Convert.ToInt32(it.Item1));
var q2 = b.AsQueryable().Select(it => (float) it.Item1);

Get delegate arguments inside delegate

Could someone please help me to understand how to get all parameters passed to delegate inside delegate itself?
I have class :
public class ShopManager : ShopEntities
{
public ShopManager getWhere(Func<Object, Object> dataList)
{
var x = dataList.???; // how to get arguments?
return this;
}
public Object getLike(Object dataValue)
{
return dataValue;
}
}
Then i call it as :
ShopManager shopManager = new ShopManager()
var demo = shopManager.getWhere(xxx => shopManager.getLike("DATA"));
The question is : how to get passed parameters "xxx" and "DATA" inside method getWhere()?
Thanks in advance.

You can't because it's the other way around. You can't get the arguments because the delegate does not hold them; the getWhere method will need to pass a value for the xxx parameter when invoking the delegate. The anonymous method that the delegate refers to will then receive this value as the xxx parameter, and in turn pass the string "DATA" as argument for the dataValue parameter when calling getLike. The argument values as such are not part of the delegate's state.
If you want to get information about the parameters as such (not their values), you can do that:
// get an array of ParameterInfo objects
var parameters = dataList.Method.GetParameters();
Console.WriteLine(parameters[0].Name); // prints "xxx"

If you use:
public ShopManager getWhere(Expression<Func<Object, Object>> dataList)
then you can divide the Expression into its subexpressions and parse them. But I'm not sure if using a delegate like you do is even the right thing.

You can't do it (easily). But I don't understand your idea. For what reason do you need to look into a dataList? This is just an anonymous method, you can call it and get results, you shouldn't need to examine or modify it at all.
What is your idea? Why not just call shopManager.getLike() ?

you can get the name of function by doing something like below.
var x = dataList.GetInvocationList().FirstOrDefault().Method.GetParameters();
sring name = x.FirstOrDefault().Name
this will print name as 'xxx'

Arguments are what you will provide while invoking the delegate via dataList(args), and not by the recipient of the invocation. If you want to provide additional information to getWhere() , you can try the following ....
public ShopManager getWhere(Func<Object, Object> dataList, params object[] additonalData)
{
// inspect the additionalData
}

Thanks for replies guys, i decided to use Expression> instead of common delegate. This allows to get both sides of expression - LHS and RHS.
For those who are interested in answer, this is it :
http://social.msdn.microsoft.com/Forums/en-US/csharpgeneral/thread/0f6ca823-dbe6-4eb6-9dd4-6ee895fd07b5?prof=required
Thanks for patience and attention.

public static List<object> GetMethodParameterValues(Delegate method)
{
var target = method.Target;
if (target == null) return null;
var fields = target.GetType().GetFields();
var valueList = fields.Select(field => field.GetValue(target)).ToList();
return valueList;
}