# Call Python Function

pkpy uses a variant of the Vectorcall protocol (PEP 590).

You can use call to invoke any python callable object, including functions, methods, classes, etc. For methods, call_method can be used.

• PyObject* call(PyObject* obj, ...)
• PyObject* call_method(PyObject* obj, StrName name, ...)

Let's create a dict object and set a key-value pair, which equals to the following python snippet.

obj = {}        # declare a `dict`
obj["a"] = 5    # set a key-value pair
print(obj["a"]) # print the value

First, create an empty dict object,

PyObject* tp = vm->builtins->attr("dict");
PyObject* obj = vm->call(tp);	// this is a `dict`

And set a key-value pair,

PyObject* _0 = py_var(vm, "a");
PyObject* _1 = py_var(vm, 5);
vm->call_method(obj, "__setitem__", _0, _1);

And get the value,

PyObject* ret = vm->call_method(obj, "__getitem__", _0);
std::cout << py_cast<int>(vm, i64);

If you want to call with dynamic number of arguments, you should use vm->vectorcall. This is a low-level, stack-based API.

1. First push the callable object to the stack.
2. Push the self object to the stack. If there is no self, push PY_NULL.
3. Push the arguments to the stack.
4. Call vm->vectorcall with the number of arguments.

PyObject* f_sum = vm->builtins->attr("sum");

List args(N);   // a list of N arguments

vm->s_data.push_back(f_print);
vm->s_data.push_back(PY_NULL);  // self

for(PyObject* arg : args) {
    vm->s_data.push_back(arg);
}

PyObject* ret = vm->vectorcall(args.size());