pybind11/example/example6.cpp

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/*
example/example6.cpp -- supporting Pythons' sequence protocol, iterators,
etc.
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Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>
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All rights reserved. Use of this source code is governed by a
BSD-style license that can be found in the LICENSE file.
*/
#include "example.h"
#include <pybind11/operators.h>
#include <pybind11/stl.h>
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class Sequence {
public:
Sequence(size_t size) : m_size(size) {
std::cout << "Value constructor: Creating a sequence with " << m_size << " entries" << std::endl;
m_data = new float[size];
memset(m_data, 0, sizeof(float) * size);
}
Sequence(const std::vector<float> &value) : m_size(value.size()) {
std::cout << "Value constructor: Creating a sequence with " << m_size << " entries" << std::endl;
m_data = new float[m_size];
memcpy(m_data, &value[0], sizeof(float) * m_size);
}
Sequence(const Sequence &s) : m_size(s.m_size) {
std::cout << "Copy constructor: Creating a sequence with " << m_size << " entries" << std::endl;
m_data = new float[m_size];
memcpy(m_data, s.m_data, sizeof(float)*m_size);
}
Sequence(Sequence &&s) : m_size(s.m_size), m_data(s.m_data) {
std::cout << "Move constructor: Creating a sequence with " << m_size << " entries" << std::endl;
s.m_size = 0;
s.m_data = nullptr;
}
~Sequence() {
std::cout << "Freeing a sequence with " << m_size << " entries" << std::endl;
delete[] m_data;
}
Sequence &operator=(const Sequence &s) {
std::cout << "Assignment operator: Creating a sequence with " << s.m_size << " entries" << std::endl;
delete[] m_data;
m_size = s.m_size;
m_data = new float[m_size];
memcpy(m_data, s.m_data, sizeof(float)*m_size);
return *this;
}
Sequence &operator=(Sequence &&s) {
std::cout << "Move assignment operator: Creating a sequence with " << s.m_size << " entries" << std::endl;
if (&s != this) {
delete[] m_data;
m_size = s.m_size;
m_data = s.m_data;
s.m_size = 0;
s.m_data = nullptr;
}
return *this;
}
bool operator==(const Sequence &s) const {
if (m_size != s.size())
return false;
for (size_t i=0; i<m_size; ++i)
if (m_data[i] != s[i])
return false;
return true;
}
bool operator!=(const Sequence &s) const {
return !operator==(s);
}
float operator[](size_t index) const {
return m_data[index];
}
float &operator[](size_t index) {
return m_data[index];
}
bool contains(float v) const {
for (size_t i=0; i<m_size; ++i)
if (v == m_data[i])
return true;
return false;
}
Sequence reversed() const {
Sequence result(m_size);
for (size_t i=0; i<m_size; ++i)
result[m_size-i-1] = m_data[i];
return result;
}
size_t size() const { return m_size; }
const float *begin() const { return m_data; }
const float *end() const { return m_data+m_size; }
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private:
size_t m_size;
float *m_data;
};
void init_ex6(py::module &m) {
py::class_<Sequence> seq(m, "Sequence");
seq.def(py::init<size_t>())
.def(py::init<const std::vector<float>&>())
/// Bare bones interface
.def("__getitem__", [](const Sequence &s, size_t i) {
if (i >= s.size())
throw py::index_error();
return s[i];
})
.def("__setitem__", [](Sequence &s, size_t i, float v) {
if (i >= s.size())
throw py::index_error();
s[i] = v;
})
.def("__len__", &Sequence::size)
/// Optional sequence protocol operations
.def("__iter__", [](const Sequence &s) { return py::make_iterator(s.begin(), s.end()); },
py::keep_alive<0, 1>() /* Essential: keep object alive while iterator exists */)
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.def("__contains__", [](const Sequence &s, float v) { return s.contains(v); })
.def("__reversed__", [](const Sequence &s) -> Sequence { return s.reversed(); })
/// Slicing protocol (optional)
.def("__getitem__", [](const Sequence &s, py::slice slice) -> Sequence* {
py::ssize_t start, stop, step, slicelength;
if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
throw py::error_already_set();
Sequence *seq = new Sequence(slicelength);
for (int i=0; i<slicelength; ++i) {
(*seq)[i] = s[start]; start += step;
}
return seq;
})
.def("__setitem__", [](Sequence &s, py::slice slice, const Sequence &value) {
py::ssize_t start, stop, step, slicelength;
if (!slice.compute(s.size(), &start, &stop, &step, &slicelength))
throw py::error_already_set();
if ((size_t) slicelength != value.size())
throw std::runtime_error("Left and right hand size of slice assignment have different sizes!");
for (int i=0; i<slicelength; ++i) {
s[start] = value[i]; start += step;
}
})
/// Comparisons
.def(py::self == py::self)
.def(py::self != py::self);
// Could also define py::self + py::self for concatenation, etc.
#if 0
// Obsolete: special data structure for exposing custom iterator types to python
// kept here for illustrative purposes because there might be some use cases which
// are not covered by the much simpler py::make_iterator
struct PySequenceIterator {
PySequenceIterator(const Sequence &seq, py::object ref) : seq(seq), ref(ref) { }
float next() {
if (index == seq.size())
throw py::stop_iteration();
return seq[index++];
}
const Sequence &seq;
py::object ref; // keep a reference
size_t index = 0;
};
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py::class_<PySequenceIterator>(seq, "Iterator")
.def("__iter__", [](PySequenceIterator &it) -> PySequenceIterator& { return it; })
.def("__next__", &PySequenceIterator::next);
On the actual Sequence object, the iterator would be constructed as follows:
.def("__iter__", [](py::object s) { return PySequenceIterator(s.cast<const Sequence &>(), s); })
#endif
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}