The intlist is a defined class, you can see two file

https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/core/ScalarType.h 15

typedef ArrayRef<int64_t> IntList;


https://github.com/pytorch/pytorch/blob/master/aten/src/ATen/core/ArrayRef.h 14

class ArrayRef final {
 public:
  using iterator = const T*;
  using const_iterator = const T*;
  using size_type = size_t;

  using reverse_iterator = std::reverse_iterator<iterator>;
...

Since it’s a internal class of pytorch, i guess it cannot be parsed by pybind11. So you can use std::vector<int64_t> arg in the arguments, then convert it to IntList by IntList val(arg).