PyNativeTypeExtractor.h

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// Mantid Repository : https://github.com/mantidproject/mantid
//
// Copyright © 2021 ISIS Rutherford Appleton Laboratory UKRI,
//   NScD Oak Ridge National Laboratory, European Spallation Source,
//   Institut Laue - Langevin & CSNS, Institute of High Energy Physics, CAS
// SPDX - License - Identifier: GPL - 3.0 +
#pragma once
#include "MantidAPI/Workspace.h"
#include "MantidKernel/Logger.h"
 
#include <boost/python/extract.hpp>
#include <boost/python/list.hpp>
#include <boost/python/object.hpp>
#include <boost/variant.hpp>
 
#include <exception>
#include <string>
#include <variant>
#include <vector>
 
namespace {
Mantid::Kernel::Logger g_log("Python Type Extractor");
}
 
namespace Mantid::PythonInterface {
 
struct PyNativeTypeExtractor {
  using PythonOutputT = boost::make_recursive_variant<bool, int, double, std::string, Mantid::API::Workspace_sptr,
                                                      std::vector<boost::recursive_variant_>>::type;
 
  static PythonOutputT convert(const boost::python::object &obj) {
    using namespace boost::python;
    PyObject *rawptr = obj.ptr();
    PythonOutputT out;
 
    if (PyList_Check(rawptr)) {
      out = handleList(obj);
    } else if (PyBool_Check(rawptr)) {
      out = extract<bool>(obj);
    } else if (PyFloat_Check(rawptr)) {
      out = extract<double>(obj);
    } else if (PyLong_Check(rawptr)) {
      out = static_cast<int>(extract<long>(obj));
    } else if (PyUnicode_Check(rawptr)) {
      out = extract<std::string>(obj);
    } else if (auto extractor = extract<Mantid::API::Workspace_sptr>(obj); extractor.check()) {
      out = extractor();
    } else {
      throw std::invalid_argument("Unrecognised Python type");
    }
    return out;
  }
 
private:
  static PythonOutputT handleList(const boost::python::object &obj) {
    auto rawptr = obj.ptr();
    auto n = PyList_Size(rawptr);
    auto vec = std::vector<PythonOutputT>();
    vec.reserve(n);
    for (Py_ssize_t i = 0; i < n; ++i) {
      vec.emplace_back(convert(obj[i]));
    }
    return vec;
  }
};
 
class IPyTypeVisitor : public boost::static_visitor<> {
public:
  virtual ~IPyTypeVisitor() = default;
  virtual void operator()(bool value) const = 0;
  virtual void operator()(int value) const = 0;
  virtual void operator()(double value) const = 0;
  virtual void operator()(std::string) const = 0;
  virtual void operator()(Mantid::API::Workspace_sptr) const = 0;
 
  virtual void operator()(std::vector<bool>) const = 0;
  virtual void operator()(std::vector<int>) const = 0;
  virtual void operator()(std::vector<double>) const = 0;
  virtual void operator()(std::vector<std::string>) const = 0;
 
  void operator()(std::vector<PyNativeTypeExtractor::PythonOutputT> const &values) const {
    if (values.size() == 0)
      return;
    const auto &elemType = values[0].type();
 
    // We must manually dispatch for container types, as boost will try
    // to recurse down to scalar values.
    if (elemType == typeid(bool)) {
      applyVectorProp<bool>(values);
    } else if (elemType == typeid(double)) {
      applyVectorProp<double>(values);
    } else if (elemType == typeid(int)) {
      applyVectorProp<int>(values);
    } else if (elemType == typeid(std::string)) {
      applyVectorProp<std::string>(values);
    } else {
      // Recurse down
      for (const auto &val : values) {
        boost::apply_visitor(*this, val);
      }
    }
  }
 
private:
  template <typename ScalarT>
  void applyVectorProp(const std::vector<Mantid::PythonInterface::PyNativeTypeExtractor::PythonOutputT> &values) const {
    std::vector<ScalarT> propVals;
    propVals.reserve(values.size());
 
    // Explicitly copy so we don't have to think about Python lifetimes with refs
    try {
 
      std::transform(values.cbegin(), values.cend(), std::back_inserter(propVals),
                     [](const Mantid::PythonInterface::PyNativeTypeExtractor::PythonOutputT &varadicVal) {
                       return boost::get<ScalarT>(varadicVal);
                     });
    } catch (boost::bad_get &e) {
      std::string err{
          "A list with mixed types is unsupported as precision loss can occur trying to determine a common type."
          " \nOriginal exception: "};
      // Boost will convert bad_get into runtime_error anyway....
      throw std::runtime_error(err + e.what());
    }
    this->operator()(std::move(propVals));
  }
};
 
} // namespace Mantid::PythonInterface