Set attributes on python objects from Go code

[ahdekkers]

Hi,

Say I have the following code:

func init() {
    py.RegisterModule(&py.ModuleImpl{
        Info: py.ModuleInfo{
        Name: "lib",
    },
    Methods: []*py.Method{
        py.MustNewMethod("get_data", getDataFunc, 0, ""),
    },
    })
}

var DataType = py.NewType("Data", "")

type Data struct {
    Items []string
}

func (*Data) Type() *py.Type {
    return DataType
}

func getDataFunc(py.Object, py.Tuple) (py.Object, error) {
    return &Data{Items: []string{"one", "two"}}, nil
}

When I try something like the following in python:

import lib

data = lib.get_data()
print(data.Items)

I get Attribute not found error on Items. How can I go about setting Items as an accessible attribute on the Data object?

I tried variations of DataType.Dict["Items"] = py.NewList() but none of these attempts worked. Any suggestions or guidance in what I may be doing wrong would be greatly appreciated.

[ahdekkers]

For anyone else who has this issue, the solution is actually quite simple. The object (in this case the "Data" struct) needs to implement Igetattribute, which has the method Mgetattribute.

[sbinet]

great that you could address your issue from "first principles" :)

perhaps this warrants a little example, though ? WDYT ?

[ahdekkers]

Sure. Here is the above code with the solution implemented.

func init() {
    py.RegisterModule(&py.ModuleImpl{
        Info: py.ModuleInfo{
        Name: "lib",
    },
    Methods: []*py.Method{
        py.MustNewMethod("get_data", getDataFunc, 0, ""),
    },
    })
}

var DataType = py.NewType("Data", "")

type Data struct {
    Items []string
}

func (*Data) Type() *py.Type {
    return DataType
}

//Here is the solution which fixes the attribute error on data.Items in the python code
func (d *Data) M__getattribute__(key string) (py.Object, error) {
    if key == "Items" {
        //Convert from Go string array to python string array
        var pyItems []py.Object
        for _, item := range d.Items {
            pyItems = append(pyItems, py.String(item))
        }
        //Return d.Items as a python object
        return py.NewListFromItems(pyItems), nil
    }

    return nil, py.ExceptionNewf(py.AttributeError, "'%s' has no attribute '%s'", p.Type().Name, key)
}

func getDataFunc(py.Object, py.Tuple) (py.Object, error) {
    return &Data{Items: []string{"one", "two"}}, nil
}