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{"@context":"https://schema.org","@type":"QAPage","mainEntity":{"@type":"Question","name":"How to pass *varargs?","text":"
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
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Here is an example in python
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>>> import numpy as np\n>>> dx=4.0\n>>> dy=5.0\n>>> zX=[[1,2,3],[4,5,6],[8,9,0]]\n>>> np.gradient(zX, dx, dy)\n[array([[ 0.75 ,  0.75 ,  0.75 ],\n       [ 0.875,  0.875, -0.375],\n       [ 1.   ,  1.   , -1.5  ]]), array([[ 0.2,  0.2,  0.2],\n       [ 0.2,  0.2,  0.2],\n       [ 0.2, -0.8, -1.8]])]\n>>>
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I tried to pass the variable args with the args tuple but then the python function complains that the number of arguments is incorrect.
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Python.Runtime.PythonException: TypeError : invalid number of arguments\n ['  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)\n   at Python.Runtime.PyObject.InvokeMethod(String name, PyTuple args, PyDict kw)\n
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I also tried to pass it as kw[\"varargs\"] but then python says there is no kwarg named \"varargs\"
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So how to call that function?
","upvoteCount":1,"answerCount":3,"acceptedAnswer":{"@type":"Answer","text":"
You can see the available overloads here: 
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\n      pythonnet/src/runtime/PythonTypes/PyObject.cs\n    
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\n        Lines 815 to 930\n      in\n      090ff9f\n    
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 /// <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; 
 } 
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So we have
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PyTuple
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params PyObject[]
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PyObject[], PyDict
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PyTuple, PyDict
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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).
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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.
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Does any of these work?
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np.gradient(zX, 4.0, 5.0) (using the fact that np is dynamic, without additional kwArgs)
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np.InvokeMethod(new PyObject[] {zX, new PyFloat(4.0), new PyFloat(5.0)}, kwArgs)
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","upvoteCount":1,"url":"https://github.com/pythonnet/pythonnet/discussions/1772#discussioncomment-2635974"}}}