Question

i need to pass a parameter list stored in a dictionary to a function
implemented by an ironPython class.

I have prepared the minimum example that reproduces the error:

        // C# Side
        var runtime = Python.CreateRuntime();
        dynamic test = runtime.UseFile("test.py");

        // Here the parameters dictionary is instantiated and filled
        var parametersDictionary = new Dictionary<string, int>();
        parametersDictionary.Add("first", 1);

        // The Python 'x' instance is called passing parameter dictionary
        var result = test.x.ReturnFirstParameter(parametersDictionary);

Now the Python code:

# Python side

# Class 'Expression' definition
class Expression(object):
    def ReturnFirstParameter(self, **parameters):
        return parameters['first']

# Class 'Expression' instantiation
x = Expression()

When i run the program, i get the following exception:

ReturnFirstParameter() takes exactly 1 argument (2 given)

The first parameter is ‘self’, but it seems like ignoring it receives
2 parameters, ‘self’ and the dictionary.

I have tried changing the dictionary for other parameters and it works well. The problem
only arises when you receive a ** parameter.

I deeply appreciate your help!

Esteban.

Answer 1

It should work to simply remove the ** from in front of parameters in the Python code:

class Expression(object):
    def ReturnFirstParameter(self, parameters):
        return parameters['first']

** should be used when you are passing in named parameters to a function, and your C# code will be passing a dictionary.

Your C# code would call the function like this:

x.ReturnFirstParameter({'first': 1})

For it to work with **parameters the call would need to be

x.ReturnFirstParameter(first=1)

There may be a way to do this with ironpython but I’m not sure how.