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How to pass *varargs?#1772

Answeredbyfilmor

henon asked this question inQ&A

henon

Apr 24, 2022

· 3 comments· 5 replies

AnsweredbyfilmorReturn to top

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henon
Apr 24, 2022

How do you pass a variable list of arguments in pythonnet? The problem is the functionnumpy.gradient(f, *varargs, axis=None, edge_order=1) as documented here:https://numpy.org/doc/stable/reference/generated/numpy.gradient.html

Here is an example in python

>>>importnumpyasnp>>>dx=4.0>>>dy=5.0>>>zX=[[1,2,3],[4,5,6],[8,9,0]]>>>np.gradient(zX,dx,dy)[array([[0.75 ,0.75 ,0.75 ],       [0.875,0.875,-0.375],       [1.   ,1.   ,-1.5  ]]),array([[0.2,0.2,0.2],       [0.2,0.2,0.2],       [0.2,-0.8,-1.8]])]>>>

I tried to pass the variable args with the args tuple but then the python function complains that the number of arguments is incorrect.

Python.Runtime.PythonException: TypeError : invalid number of arguments ['  File "C:\\Users\\henon\\AppData\\Local\\python-3.7.3-embed-amd64\\lib\\numpy\\lib\\function_base.py", line 1013, in gradient\n    raise TypeError("invalid number of arguments")\n']   at Python.Runtime.PyObject.Invoke(PyTuple args, PyDict kw)   at Python.Runtime.PyObject.InvokeMethod(String name, PyTuple args, PyDict kw)

I also tried to pass it as kw["varargs"] but then python says there is no kwarg named "varargs"

So how to call that function?

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Answered by filmor

Apr 26, 2022

You can see the available overloads here:

pythonnet/src/runtime/PythonTypes/PyObject.cs

Lines 815 to 930 in090ff9f

	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(stringname,paramsPyObject[]args)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));
	if(args.Contains(null))thrownewArgumentNullException();

	PyObjectmethod=GetAttr(name);

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Replies: 3 comments 5 replies

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henon
Apr 25, 2022
Author

I have an update, looks like I can pass a second tuple after the args tuple and then I am getting a different error so this is a step in the right direction. But I am still stumped as to what the function really expects

using(Py.GIL()){dynamicnp=Py.Import("numpy");dynamiczX=np.array(new[,]{{1,2,3},{4,5,6},{8,9,0}});Console.WriteLine(zX.__repr__());varresult=(npasPyObject).InvokeMethod("gradient",newPyTuple(newPyObject[]{zXasPyObject}),newPyTuple(newPyObject[]{newPyFloat(4.0),newPyFloat(5.0),}));Console.WriteLine(result.InvokeMethod("__repr__"));}

Exception:

Python.Runtime.PythonException: ValueError : when 1d, distances must match the length of the corresponding dimension ['  File "C:\\Users\\henon\\AppData\\Local\\python-3.7.3-embed-amd64\\lib\\numpy\\lib\\function_base.py", line 1004, in gradient\n    raise ValueError("when 1d, distances must match "\n']   at Python.Runtime.PyObject.Invoke(PyObject[] args)   at Python.Runtime.PyObject.InvokeMethod(String name, PyObject[] args)

Any ideas@filmor ?

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henon Apr 25, 2022
Author

Nah, looks like the second tuple is interpreted as kwargs because I can't pass additional kw args:

varresult=(npasPyObject).InvokeMethod("gradient",newPyTuple(newPyObject[]{zXasPyObject}),newPyTuple(newPyObject[]{newPyFloat(4.0),newPyFloat(5.0),}),newPyDict(){["edge_order"]=newPyInt(1)});

This again leads to invalid arguments errorPython.Runtime.PythonException: TypeError : invalid number of arguments

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lostmsu
Apr 25, 2022
Maintainer

This should work according to my understanding:

InvokeMethod('gradient',newPyTuple(f,varArg1,varArg2),kwArgs)

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henon Apr 25, 2022
Author

Yeah, that was what I would have expected too but it does not. That was what I tried initially. It givesTypeError : invalid number of arguments
I am getting the feeling this is a bug.

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filmor
Apr 26, 2022
Maintainer

You can see the available overloads here:

pythonnet/src/runtime/PythonTypes/PyObject.cs

Lines 815 to 930 in090ff9f

	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(stringname,paramsPyObject[]args)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));
	if(args.Contains(null))thrownewArgumentNullException();

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args);
	method.Dispose();
	returnresult;
	}


	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(stringname,PyTupleargs)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args);
	method.Dispose();
	returnresult;
	}

	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(PyObjectname,paramsPyObject[]args)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));
	if(args.Contains(null))thrownewArgumentNullException();

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args);
	method.Dispose();
	returnresult;
	}


	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(PyObjectname,PyTupleargs)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args);
	method.Dispose();
	returnresult;
	}


	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments
	/// and keyword arguments. Keyword args are passed as a PyDict object.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(stringname,PyObject[]args,PyDict?kw)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));
	if(args.Contains(null))thrownewArgumentNullException();

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args,kw);
	method.Dispose();
	returnresult;
	}


	/// <summary>
	/// InvokeMethod Method
	/// </summary>
	/// <remarks>
	/// Invoke the named method of the object with the given arguments
	/// and keyword arguments. Keyword args are passed as a PyDict object.
	/// A PythonException is raised if the invocation is unsuccessful.
	/// </remarks>
	publicPyObjectInvokeMethod(stringname,PyTupleargs,PyDict?kw)
	{
	if(name==null)thrownewArgumentNullException(nameof(name));
	if(args==null)thrownewArgumentNullException(nameof(args));

	PyObjectmethod=GetAttr(name);
	PyObjectresult=method.Invoke(args,kw);
	method.Dispose();
	returnresult;
	}

So we have

PyTuple
params PyObject[]
PyObject[], PyDict
PyTuple, PyDict

It's not ideal as it only has overloads with aPyObject name for the first two functions and the .NET varargs will probably hide the singlePyTuple overload (not sure about that).

I'm not sure why you'd think any of your attempts here should work. The variant given by@lostmsu could maybe also run into selecting the wrong overload (theparams one), I'd have to check the rules.

Does any of these work?

np.gradient(zX, 4.0, 5.0) (using the fact thatnp isdynamic, without additionalkwArgs)
np.InvokeMethod(new PyObject[] {zX, new PyFloat(4.0), new PyFloat(5.0)}, kwArgs)

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henon Apr 26, 2022
Author

Thanks for your time looking into this. Both your suggestions don't work. The dynamic version givesPython.Runtime.PythonException: TypeError : invalid number of arguments as does the second option. Do you think pythonnet is missing an overload for this kind of python function?

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henon May 30, 2022
Author

I reopened this as an issue, as it is impossible to pass the *varargs.#1804

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henon May 31, 2022
Author

OK, I was wrong,@filmor 's answer works with the current preview version of pythonnet, it just had a typo. The working code is:

varkwArgs=newPyDict(){["edge_order"]=newPyInt(1)};varresult=(npasPyObject).InvokeMethod("gradient",newPyObject[]{(zXasPyObject),newPyFloat(4.0),newPyFloat(5.0)},kwArgs);

Answer selected byhenon

Movatterモバイル変換

How to pass *varargs?#1772

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henonApr 24, 2022

Replies: 3 comments· 5 replies

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henonApr 25, 2022 Author

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henonApr 25, 2022 Author

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lostmsuApr 25, 2022 Maintainer

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henonApr 25, 2022 Author

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filmorApr 26, 2022 Maintainer

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henonApr 26, 2022 Author

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henonMay 30, 2022 Author

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henonMay 31, 2022 Author

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henon
Apr 24, 2022

Replies: 3 comments 5 replies

henon
Apr 25, 2022
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henon Apr 25, 2022
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lostmsu
Apr 25, 2022
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henon Apr 25, 2022
Author

filmor
Apr 26, 2022
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henon Apr 26, 2022
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henon May 30, 2022
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henon May 31, 2022
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