pytorch/torch/csrc/utils/six.h

#pragma once

#include <pybind11/pybind11.h>
#include <torch/csrc/utils/structseq.h>
#include <torch/csrc/utils/object_ptr.h>

namespace six {

// Usually instances of PyStructSequence is also an instance of tuple
// but in some py2 environment it is not, so we have to manually check
// the name of the type to determine if it is a namedtupled returned
// by a pytorch operator.

inline bool isStructSeq(pybind11::handle input) {
  return pybind11::cast<std::string>(input.get_type().attr("__module__")) == "torch.return_types";
}

inline bool isStructSeq(PyObject* obj) {
  return isStructSeq(pybind11::handle(obj));
}

inline bool isTuple(pybind11::handle input) {
  if (PyTuple_Check(input.ptr())) {
    return true;
  }
#if PY_MAJOR_VERSION == 2
  return isStructSeq(input);
#else
  return false;
#endif
}

inline bool isTuple(PyObject* obj) {
  return isTuple(pybind11::handle(obj));
}

// maybeAsTuple: if the input is a structseq, then convert it to a tuple
//
// On Python 3, structseq is a subtype of tuple, so these APIs could be used directly.
// But on Python 2, structseq is not a subtype of tuple, so we need to manually create a
// new tuple object from structseq.
inline THPObjectPtr maybeAsTuple(PyStructSequence *obj) {
#if PY_MAJOR_VERSION == 2
  return THPObjectPtr(torch::utils::structseq_slice(obj, 0, Py_SIZE(obj)));
#else
  Py_INCREF(obj);
  return THPObjectPtr((PyObject *)obj);
#endif
}

inline THPObjectPtr maybeAsTuple(PyObject *obj) {
  if (isStructSeq(obj))
    return maybeAsTuple((PyStructSequence *)obj);
  Py_INCREF(obj);
  return THPObjectPtr(obj);
}

}  // namespace six