How to pass *varargs? #1772

henon · 2022-04-24T20:54:00Z

henon
Apr 24, 2022

How do you pass a variable list of arguments in pythonnet? The problem is the function numpy.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

>>> import numpy as np
>>> 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?

Answered by filmor

Apr 26, 2022

You can see the available overloads here:

pythonnet/src/runtime/PythonTypes/PyObject.cs

Lines 815 to 930 in 090ff9f

     /// <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>  
   public PyObject InvokeMethod(string name, params PyObject[] args)  
   {  
   if (name == null) throw new ArgumentNullException(nameof(name));  
   if (args == null) throw new ArgumentNullException(nameof(args));  
   if (args.Contains(null)) throw new ArgumentNullException();  
    
   PyObject method = GetAttr(name);

View full answer

henon · 2022-04-25T10:01:08Z

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()) {
                dynamic np = Py.Import("numpy");
                dynamic zX = np.array(new[,] { { 1, 2, 3 }, { 4, 5, 6 }, { 8, 9, 0 } });
                Console.WriteLine(zX.__repr__());
               var result=(np as PyObject).InvokeMethod("gradient", 
                       new PyTuple(new PyObject[] { zX as PyObject}), 
                       new PyTuple(new PyObject[] { new PyFloat(4.0), new PyFloat(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 ?

1 reply

henon Apr 25, 2022
Author

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

                var result=(np as PyObject).InvokeMethod("gradient", 
                        new PyTuple(new PyObject[] { zX as PyObject}), 
                        new PyTuple(new PyObject[] { new PyFloat(4.0), new PyFloat(5.0), }),
                        new PyDict() { ["edge_order"]=new PyInt(1) }
                );

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

lostmsu · 2022-04-25T16:46:02Z

lostmsu
Apr 25, 2022
Maintainer

This should work according to my understanding:

InvokeMethod('gradient', new PyTuple(f, varArg1, varArg2), kwArgs)

1 reply

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 gives TypeError : invalid number of arguments
I am getting the feeling this is a bug.

filmor · 2022-04-26T05:33:14Z

filmor
Apr 26, 2022
Maintainer

You can see the available overloads here:

pythonnet/src/runtime/PythonTypes/PyObject.cs

Lines 815 to 930 in 090ff9f

    
           /// <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> 
        
           public PyObject InvokeMethod(string name, params PyObject[] args) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               if (args.Contains(null)) throw new ArgumentNullException(); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args); 
        
               method.Dispose(); 
        
               return result; 
        
           } 
        
           /// <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> 
        
           public PyObject InvokeMethod(string name, PyTuple args) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args); 
        
               method.Dispose(); 
        
               return result; 
        
           } 
        
           /// <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> 
        
           public PyObject InvokeMethod(PyObject name, params PyObject[] args) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               if (args.Contains(null)) throw new ArgumentNullException(); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args); 
        
               method.Dispose(); 
        
               return result; 
        
           } 
        
           /// <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> 
        
           public PyObject InvokeMethod(PyObject name, PyTuple args) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args); 
        
               method.Dispose(); 
        
               return result; 
        
           } 
        
           /// <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> 
        
           public PyObject InvokeMethod(string name, PyObject[] args, PyDict? kw) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               if (args.Contains(null)) throw new ArgumentNullException(); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args, kw); 
        
               method.Dispose(); 
        
               return result; 
        
           } 
        
           /// <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> 
        
           public PyObject InvokeMethod(string name, PyTuple args, PyDict? kw) 
        
           { 
        
               if (name == null) throw new ArgumentNullException(nameof(name)); 
        
               if (args == null) throw new ArgumentNullException(nameof(args)); 
        
               PyObject method = GetAttr(name); 
        
               PyObject result = method.Invoke(args, kw); 
        
               method.Dispose(); 
        
               return result; 
        
           }

So we have

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

It's not ideal as it only has overloads with a PyObject name for the first two functions and the .NET varargs will probably hide the single PyTuple 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 (the params one), I'd have to check the rules.

Does any of these work?

np.gradient(zX, 4.0, 5.0) (using the fact that np is dynamic, without additional kwArgs)
np.InvokeMethod(new PyObject[] {zX, new PyFloat(4.0), new PyFloat(5.0)}, kwArgs)

3 replies

henon Apr 26, 2022
Author

Thanks for your time looking into this. Both your suggestions don't work. The dynamic version gives Python.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?

henon May 30, 2022
Author

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

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:

var kwArgs = new PyDict() { ["edge_order"] = new PyInt(1) };
var result = (np as PyObject).InvokeMethod("gradient", new PyObject[] { (zX as PyObject), new PyFloat(4.0), new PyFloat(5.0) }, kwArgs );

	/// <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>
	public PyObject InvokeMethod(string name, params PyObject[] args)
	{
	if (name == null) throw new ArgumentNullException(nameof(name));
	if (args == null) throw new ArgumentNullException(nameof(args));
	if (args.Contains(null)) throw new ArgumentNullException();

	PyObject method = GetAttr(name);

How to pass *varargs? #1772

Uh oh!

henon Apr 24, 2022

Replies: 3 comments · 5 replies

Uh oh!

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henon Apr 25, 2022 Author

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henon Apr 25, 2022 Author

Uh oh!

lostmsu Apr 25, 2022 Maintainer

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henon Apr 25, 2022 Author

Uh oh!

filmor Apr 26, 2022 Maintainer

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henon Apr 26, 2022 Author

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henon May 30, 2022 Author

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Uh oh!

henon May 31, 2022 Author

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henon
Apr 24, 2022

Replies: 3 comments 5 replies

henon
Apr 25, 2022
Author

henon Apr 25, 2022
Author

lostmsu
Apr 25, 2022
Maintainer

henon Apr 25, 2022
Author

filmor
Apr 26, 2022
Maintainer

henon Apr 26, 2022
Author

henon May 30, 2022
Author

henon May 31, 2022
Author