pybind11/include/pybind11/pytypes.h

/*
    pybind11/typeid.h: Convenience wrapper classes for basic Python types

    Copyright (c) 2016 Wenzel Jakob <wenzel.jakob@epfl.ch>

    All rights reserved. Use of this source code is governed by a
    BSD-style license that can be found in the LICENSE file.
*/

#pragma once

#include "common.h"
#include <utility>
#include <type_traits>

NAMESPACE_BEGIN(pybind11)

/* A few forward declarations */
class handle; class object;
class str; class iterator;
struct arg; struct arg_v;

NAMESPACE_BEGIN(detail)
class args_proxy;

// Accessor forward declarations
template <typename Policy> class accessor;
namespace accessor_policies {
    struct obj_attr;
    struct str_attr;
    struct generic_item;
    struct sequence_item;
    struct list_item;
    struct tuple_item;
}
using obj_attr_accessor = accessor<accessor_policies::obj_attr>;
using str_attr_accessor = accessor<accessor_policies::str_attr>;
using item_accessor = accessor<accessor_policies::generic_item>;
using sequence_accessor = accessor<accessor_policies::sequence_item>;
using list_accessor = accessor<accessor_policies::list_item>;
using tuple_accessor = accessor<accessor_policies::tuple_item>;

/// Tag and check to identify a class which implements the Python object API
class pyobject_tag { };
template <typename T> using is_pyobject = std::is_base_of<pyobject_tag, T>;

/// Mixin which adds common functions to handle, object and various accessors.
/// The only requirement for `Derived` is to implement `PyObject *Derived::ptr() const`.
template <typename Derived>
class object_api : public pyobject_tag {
    const Derived &derived() const { return static_cast<const Derived &>(*this); }

public:
    iterator begin() const;
    iterator end() const;
    item_accessor operator[](handle key) const;
    item_accessor operator[](const char *key) const;
    obj_attr_accessor attr(handle key) const;
    str_attr_accessor attr(const char *key) const;
    args_proxy operator*() const;
    template <typename T> bool contains(T &&key) const;

    template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
    object operator()(Args &&...args) const;
    template <return_value_policy policy = return_value_policy::automatic_reference, typename... Args>
    PYBIND11_DEPRECATED("call(...) was deprecated in favor of operator()(...)")
        object call(Args&&... args) const;

    bool is_none() const { return derived().ptr() == Py_None; }
    pybind11::str str() const;
    pybind11::str repr() const;

    int ref_count() const { return static_cast<int>(Py_REFCNT(derived().ptr())); }
    handle get_type() const;
};

NAMESPACE_END(detail)

/// Holds a reference to a Python object (no reference counting)
class handle : public detail::object_api<handle> {
public:
    handle() = default;
    handle(PyObject *ptr) : m_ptr(ptr) { }

    PyObject *ptr() const { return m_ptr; }
    PyObject *&ptr() { return m_ptr; }
    const handle& inc_ref() const { Py_XINCREF(m_ptr); return *this; }
    const handle& dec_ref() const { Py_XDECREF(m_ptr); return *this; }

    template <typename T> T cast() const;
    explicit operator bool() const { return m_ptr != nullptr; }
    bool operator==(const handle &h) const { return m_ptr == h.m_ptr; }
    bool operator!=(const handle &h) const { return m_ptr != h.m_ptr; }
    bool check() const { return m_ptr != nullptr; }
protected:
    PyObject *m_ptr = nullptr;
};

/// Holds a reference to a Python object (with reference counting)
class object : public handle {
public:
    object() = default;
    object(const object &o) : handle(o) { inc_ref(); }
    object(const handle &h, bool borrowed) : handle(h) { if (borrowed) inc_ref(); }
    object(PyObject *ptr, bool borrowed) : handle(ptr) { if (borrowed) inc_ref(); }
    object(object &&other) noexcept { m_ptr = other.m_ptr; other.m_ptr = nullptr; }
    ~object() { dec_ref(); }

    handle release() {
      PyObject *tmp = m_ptr;
      m_ptr = nullptr;
      return handle(tmp);
    }

    object& operator=(const object &other) {
        other.inc_ref();
        dec_ref();
        m_ptr = other.m_ptr;
        return *this;
    }

    object& operator=(object &&other) noexcept {
        if (this != &other) {
            handle temp(m_ptr);
            m_ptr = other.m_ptr;
            other.m_ptr = nullptr;
            temp.dec_ref();
        }
        return *this;
    }

    // Calling cast() on an object lvalue just copies (via handle::cast)
    template <typename T> T cast() const &;
    // Calling on an object rvalue does a move, if needed and/or possible
    template <typename T> T cast() &&;
};

inline bool hasattr(handle obj, handle name) {
    return PyObject_HasAttr(obj.ptr(), name.ptr()) == 1;
}

inline bool hasattr(handle obj, const char *name) {
    return PyObject_HasAttrString(obj.ptr(), name) == 1;
}

inline object getattr(handle obj, handle name) {
    PyObject *result = PyObject_GetAttr(obj.ptr(), name.ptr());
    if (!result) { throw error_already_set(); }
    return {result, false};
}

inline object getattr(handle obj, const char *name) {
    PyObject *result = PyObject_GetAttrString(obj.ptr(), name);
    if (!result) { throw error_already_set(); }
    return {result, false};
}

inline object getattr(handle obj, handle name, handle default_) {
    if (PyObject *result = PyObject_GetAttr(obj.ptr(), name.ptr())) {
        return {result, false};
    } else {
        PyErr_Clear();
        return {default_, true};
    }
}

inline object getattr(handle obj, const char *name, handle default_) {
    if (PyObject *result = PyObject_GetAttrString(obj.ptr(), name)) {
        return {result, false};
    } else {
        PyErr_Clear();
        return {default_, true};
    }
}

inline void setattr(handle obj, handle name, handle value) {
    if (PyObject_SetAttr(obj.ptr(), name.ptr(), value.ptr()) != 0) { throw error_already_set(); }
}

inline void setattr(handle obj, const char *name, handle value) {
    if (PyObject_SetAttrString(obj.ptr(), name, value.ptr()) != 0) { throw error_already_set(); }
}

NAMESPACE_BEGIN(detail)
inline handle get_function(handle value) {
    if (value) {
#if PY_MAJOR_VERSION >= 3
        if (PyInstanceMethod_Check(value.ptr()))
            value = PyInstanceMethod_GET_FUNCTION(value.ptr());
#endif
        if (PyMethod_Check(value.ptr()))
            value = PyMethod_GET_FUNCTION(value.ptr());
    }
    return value;
}

template <typename Policy>
class accessor : public object_api<accessor<Policy>> {
    using key_type = typename Policy::key_type;

public:
    accessor(handle obj, key_type key) : obj(obj), key(std::move(key)) { }

    void operator=(const accessor &a) && { std::move(*this).operator=(handle(a)); }
    void operator=(const accessor &a) & { operator=(handle(a)); }
    void operator=(const object &o) && { std::move(*this).operator=(handle(o)); }
    void operator=(const object &o) & { operator=(handle(o)); }
    void operator=(handle value) && { Policy::set(obj, key, value); }
    void operator=(handle value) & { get_cache() = object(value, true); }

    template <typename T = Policy>
    PYBIND11_DEPRECATED("Use of obj.attr(...) as bool is deprecated in favor of pybind11::hasattr(obj, ...)")
    operator enable_if_t<std::is_same<T, accessor_policies::str_attr>::value ||
            std::is_same<T, accessor_policies::obj_attr>::value, bool>() const {
        return hasattr(obj, key);
    }
    template <typename T = Policy>
    PYBIND11_DEPRECATED("Use of obj[key] as bool is deprecated in favor of obj.contains(key)")
    operator enable_if_t<std::is_same<T, accessor_policies::generic_item>::value, bool>() const {
        return obj.contains(key);
    }

    operator object() const { return get_cache(); }
    PyObject *ptr() const { return get_cache().ptr(); }
    template <typename T> T cast() const { return get_cache().template cast<T>(); }

private:
    object &get_cache() const {
        if (!cache) { cache = Policy::get(obj, key); }
        return cache;
    }

private:
    handle obj;
    key_type key;
    mutable object cache;
};

NAMESPACE_BEGIN(accessor_policies)
struct obj_attr {
    using key_type = object;
    static object get(handle obj, handle key) { return getattr(obj, key); }
    static void set(handle obj, handle key, handle val) { setattr(obj, key, val); }
};

struct str_attr {
    using key_type = const char *;
    static object get(handle obj, const char *key) { return getattr(obj, key); }
    static void set(handle obj, const char *key, handle val) { setattr(obj, key, val); }
};

struct generic_item {
    using key_type = object;

    static object get(handle obj, handle key) {
        PyObject *result = PyObject_GetItem(obj.ptr(), key.ptr());
        if (!result) { throw error_already_set(); }
        return {result, false};
    }

    static void set(handle obj, handle key, handle val) {
        if (PyObject_SetItem(obj.ptr(), key.ptr(), val.ptr()) != 0) { throw error_already_set(); }
    }
};

struct sequence_item {
    using key_type = size_t;

    static object get(handle obj, size_t index) {
        PyObject *result = PySequence_GetItem(obj.ptr(), static_cast<ssize_t>(index));
        if (!result) { throw error_already_set(); }
        return {result, true};
    }

    static void set(handle obj, size_t index, handle val) {
        // PySequence_SetItem does not steal a reference to 'val'
        if (PySequence_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.ptr()) != 0) {
            throw error_already_set();
        }
    }
};

struct list_item {
    using key_type = size_t;

    static object get(handle obj, size_t index) {
        PyObject *result = PyList_GetItem(obj.ptr(), static_cast<ssize_t>(index));
        if (!result) { throw error_already_set(); }
        return {result, true};
    }

    static void set(handle obj, size_t index, handle val) {
        // PyList_SetItem steals a reference to 'val'
        if (PyList_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
            throw error_already_set();
        }
    }
};

struct tuple_item {
    using key_type = size_t;

    static object get(handle obj, size_t index) {
        PyObject *result = PyTuple_GetItem(obj.ptr(), static_cast<ssize_t>(index));
        if (!result) { throw error_already_set(); }
        return {result, true};
    }

    static void set(handle obj, size_t index, handle val) {
        // PyTuple_SetItem steals a reference to 'val'
        if (PyTuple_SetItem(obj.ptr(), static_cast<ssize_t>(index), val.inc_ref().ptr()) != 0) {
            throw error_already_set();
        }
    }
};
NAMESPACE_END(accessor_policies)

struct dict_iterator {
public:
    explicit dict_iterator(handle dict = handle(), ssize_t pos = -1) : dict(dict), pos(pos) { }
    dict_iterator& operator++() {
        if (!PyDict_Next(dict.ptr(), &pos, &key.ptr(), &value.ptr()))
            pos = -1;
        return *this;
    }
    std::pair<handle, handle> operator*() const {
        return std::make_pair(key, value);
    }
    bool operator==(const dict_iterator &it) const { return it.pos == pos; }
    bool operator!=(const dict_iterator &it) const { return it.pos != pos; }
private:
    handle dict, key, value;
    ssize_t pos = 0;
};

inline bool PyIterable_Check(PyObject *obj) {
    PyObject *iter = PyObject_GetIter(obj);
    if (iter) {
        Py_DECREF(iter);
        return true;
    } else {
        PyErr_Clear();
        return false;
    }
}

inline bool PyNone_Check(PyObject *o) { return o == Py_None; }

inline bool PyUnicode_Check_Permissive(PyObject *o) { return PyUnicode_Check(o) || PYBIND11_BYTES_CHECK(o); }

class kwargs_proxy : public handle {
public:
    explicit kwargs_proxy(handle h) : handle(h) { }
};

class args_proxy : public handle {
public:
    explicit args_proxy(handle h) : handle(h) { }
    kwargs_proxy operator*() const { return kwargs_proxy(*this); }
};

/// Python argument categories (using PEP 448 terms)
template <typename T> using is_keyword = std::is_base_of<arg, T>;
template <typename T> using is_s_unpacking = std::is_same<args_proxy, T>; // * unpacking
template <typename T> using is_ds_unpacking = std::is_same<kwargs_proxy, T>; // ** unpacking
template <typename T> using is_positional = bool_constant<
    !is_keyword<T>::value && !is_s_unpacking<T>::value && !is_ds_unpacking<T>::value
>;
template <typename T> using is_keyword_or_ds = bool_constant<
    is_keyword<T>::value || is_ds_unpacking<T>::value
>;

// Call argument collector forward declarations
template <return_value_policy policy = return_value_policy::automatic_reference>
class simple_collector;
template <return_value_policy policy = return_value_policy::automatic_reference>
class unpacking_collector;

NAMESPACE_END(detail)

#define PYBIND11_OBJECT_CVT(Name, Parent, CheckFun, CvtStmt) \
    public: \
        Name(const handle &h, bool borrowed) : Parent(h, borrowed) { CvtStmt; } \
        /* These are deliberately not 'explicit' to allow implicit conversion from object: */ \
        Name(const object& o): Parent(o) { CvtStmt; } \
        Name(object&& o) noexcept : Parent(std::move(o)) { CvtStmt; } \
        Name& operator=(object&& o) noexcept { (void) object::operator=(std::move(o)); CvtStmt; return *this; } \
        Name& operator=(const object& o) { return static_cast<Name&>(object::operator=(o)); CvtStmt; } \
        bool check() const { return m_ptr != nullptr && (bool) CheckFun(m_ptr); }

#define PYBIND11_OBJECT(Name, Parent, CheckFun) \
    PYBIND11_OBJECT_CVT(Name, Parent, CheckFun, )

#define PYBIND11_OBJECT_DEFAULT(Name, Parent, CheckFun) \
    PYBIND11_OBJECT(Name, Parent, CheckFun) \
    Name() : Parent() { }

class iterator : public object {
public:
    PYBIND11_OBJECT_CVT(iterator, object, PyIter_Check, value = object(); ready = false)
    iterator() : object(), value(object()), ready(false) { }
    iterator(const iterator& it) : object(it), value(it.value), ready(it.ready) { }
    iterator(iterator&& it) : object(std::move(it)), value(std::move(it.value)), ready(it.ready) { }

    /** Caveat: this copy constructor does not (and cannot) clone the internal
        state of the Python iterable */
    iterator &operator=(const iterator &it) {
        (void) object::operator=(it);
        value = it.value;
        ready = it.ready;
        return *this;
    }

    iterator &operator=(iterator &&it) noexcept {
        (void) object::operator=(std::move(it));
        value = std::move(it.value);
        ready = it.ready;
        return *this;
    }

    iterator& operator++() {
        if (m_ptr)
            advance();
        return *this;
    }

    /** Caveat: this postincrement operator does not (and cannot) clone the
        internal state of the Python iterable. It should only be used to
        retrieve the current iterate using <tt>operator*()</tt> */
    iterator operator++(int) {
        iterator rv(*this);
        rv.value = value;
        if (m_ptr)
            advance();
        return rv;
    }

    bool operator==(const iterator &it) const { return *it == **this; }
    bool operator!=(const iterator &it) const { return *it != **this; }

    handle operator*() const {
        if (!ready && m_ptr) {
            auto& self = const_cast<iterator &>(*this);
            self.advance();
            self.ready = true;
        }
        return value;
    }

private:
    void advance() { value = object(PyIter_Next(m_ptr), false); }

private:
    object value;
    bool ready;
};

class iterable : public object {
public:
    PYBIND11_OBJECT_DEFAULT(iterable, object, detail::PyIterable_Check)
};

class bytes;

class str : public object {
public:
    PYBIND11_OBJECT_DEFAULT(str, object, detail::PyUnicode_Check_Permissive)

    str(const char *c, size_t n)
    : object(PyUnicode_FromStringAndSize(c, (ssize_t) n), false) {
        if (!m_ptr) pybind11_fail("Could not allocate string object!");
    }

    // 'explicit' is explicitly omitted from the following constructors to allow implicit conversion to py::str from C++ string-like objects
    str(const char *c)
        : object(PyUnicode_FromString(c), false) {
        if (!m_ptr) pybind11_fail("Could not allocate string object!");
    }

    str(const std::string &s) : str(s.data(), s.size()) { }

    explicit str(const bytes &b);

    operator std::string() const {
        object temp = *this;
        if (PyUnicode_Check(m_ptr)) {
            temp = object(PyUnicode_AsUTF8String(m_ptr), false);
            if (!temp)
                pybind11_fail("Unable to extract string contents! (encoding issue)");
        }
        char *buffer;
        ssize_t length;
        if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
            pybind11_fail("Unable to extract string contents! (invalid type)");
        return std::string(buffer, (size_t) length);
    }

    template <typename... Args>
    str format(Args &&...args) const {
        return attr("format")(std::forward<Args>(args)...);
    }
};

inline namespace literals {
/// String literal version of str
inline str operator"" _s(const char *s, size_t size) { return {s, size}; }
}

class bytes : public object {
public:
    PYBIND11_OBJECT_DEFAULT(bytes, object, PYBIND11_BYTES_CHECK)

    // Allow implicit conversion:
    bytes(const char *c)
    : object(PYBIND11_BYTES_FROM_STRING(c), false) {
        if (!m_ptr) pybind11_fail("Could not allocate bytes object!");
    }

    bytes(const char *c, size_t n)
    : object(PYBIND11_BYTES_FROM_STRING_AND_SIZE(c, (ssize_t) n), false) {
        if (!m_ptr) pybind11_fail("Could not allocate bytes object!");
    }

    // Allow implicit conversion:
    bytes(const std::string &s) : bytes(s.data(), s.size()) { }

    explicit bytes(const pybind11::str &s);

    operator std::string() const {
        char *buffer;
        ssize_t length;
        if (PYBIND11_BYTES_AS_STRING_AND_SIZE(m_ptr, &buffer, &length))
            pybind11_fail("Unable to extract bytes contents!");
        return std::string(buffer, (size_t) length);
    }
};

inline bytes::bytes(const pybind11::str &s) {
    object temp = s;
    if (PyUnicode_Check(s.ptr())) {
        temp = object(PyUnicode_AsUTF8String(s.ptr()), false);
        if (!temp)
            pybind11_fail("Unable to extract string contents! (encoding issue)");
    }
    char *buffer;
    ssize_t length;
    if (PYBIND11_BYTES_AS_STRING_AND_SIZE(temp.ptr(), &buffer, &length))
        pybind11_fail("Unable to extract string contents! (invalid type)");
    auto obj = object(PYBIND11_BYTES_FROM_STRING_AND_SIZE(buffer, length), false);
    if (!obj)
        pybind11_fail("Could not allocate bytes object!");
    m_ptr = obj.release().ptr();
}

inline str::str(const bytes& b) {
    char *buffer;
    ssize_t length;
    if (PYBIND11_BYTES_AS_STRING_AND_SIZE(b.ptr(), &buffer, &length))
        pybind11_fail("Unable to extract bytes contents!");
    auto obj = object(PyUnicode_FromStringAndSize(buffer, (ssize_t) length), false);
    if (!obj)
        pybind11_fail("Could not allocate string object!");
    m_ptr = obj.release().ptr();
}

class none : public object {
public:
    PYBIND11_OBJECT(none, object, detail::PyNone_Check)
    none() : object(Py_None, true) { }
};

class bool_ : public object {
public:
    PYBIND11_OBJECT_DEFAULT(bool_, object, PyBool_Check)
    // Allow implicit conversion from and to `bool`:
    bool_(bool value) : object(value ? Py_True : Py_False, true) { }
    operator bool() const { return m_ptr && PyLong_AsLong(m_ptr) != 0; }
};

class int_ : public object {
public:
    PYBIND11_OBJECT_DEFAULT(int_, object, PYBIND11_LONG_CHECK)
    // Allow implicit conversion from C++ integral types:
    template <typename T,
              detail::enable_if_t<std::is_integral<T>::value, int> = 0>
    int_(T value) {
        if (sizeof(T) <= sizeof(long)) {
            if (std::is_signed<T>::value)
                m_ptr = PyLong_FromLong((long) value);
            else
                m_ptr = PyLong_FromUnsignedLong((unsigned long) value);
        } else {
            if (std::is_signed<T>::value)
                m_ptr = PyLong_FromLongLong((long long) value);
            else
                m_ptr = PyLong_FromUnsignedLongLong((unsigned long long) value);
        }
        if (!m_ptr) pybind11_fail("Could not allocate int object!");
    }

    template <typename T,
              detail::enable_if_t<std::is_integral<T>::value, int> = 0>
    operator T() const {
        if (sizeof(T) <= sizeof(long)) {
            if (std::is_signed<T>::value)
                return (T) PyLong_AsLong(m_ptr);
            else
                return (T) PyLong_AsUnsignedLong(m_ptr);
        } else {
            if (std::is_signed<T>::value)
                return (T) PYBIND11_LONG_AS_LONGLONG(m_ptr);
            else
                return (T) PYBIND11_LONG_AS_UNSIGNED_LONGLONG(m_ptr);
        }
    }
};

class float_ : public object {
public:
    PYBIND11_OBJECT_DEFAULT(float_, object, PyFloat_Check)
    // Allow implicit conversion from float/double:
    float_(float value) : object(PyFloat_FromDouble((double) value), false) {
        if (!m_ptr) pybind11_fail("Could not allocate float object!");
    }
    float_(double value) : object(PyFloat_FromDouble((double) value), false) {
        if (!m_ptr) pybind11_fail("Could not allocate float object!");
    }
    operator float() const { return (float) PyFloat_AsDouble(m_ptr); }
    operator double() const { return (double) PyFloat_AsDouble(m_ptr); }
};

class weakref : public object {
public:
    PYBIND11_OBJECT_DEFAULT(weakref, object, PyWeakref_Check)
    explicit weakref(handle obj, handle callback = handle()) : object(PyWeakref_NewRef(obj.ptr(), callback.ptr()), false) {
        if (!m_ptr) pybind11_fail("Could not allocate weak reference!");
    }
};

class slice : public object {
public:
    PYBIND11_OBJECT_DEFAULT(slice, object, PySlice_Check)
    slice(ssize_t start_, ssize_t stop_, ssize_t step_) {
        int_ start(start_), stop(stop_), step(step_);
        m_ptr = PySlice_New(start.ptr(), stop.ptr(), step.ptr());
        if (!m_ptr) pybind11_fail("Could not allocate slice object!");
    }
    bool compute(size_t length, size_t *start, size_t *stop, size_t *step,
                 size_t *slicelength) const {
        return PySlice_GetIndicesEx((PYBIND11_SLICE_OBJECT *) m_ptr,
                                    (ssize_t) length, (ssize_t *) start,
                                    (ssize_t *) stop, (ssize_t *) step,
                                    (ssize_t *) slicelength) == 0;
    }
};

class capsule : public object {
public:
    PYBIND11_OBJECT_DEFAULT(capsule, object, PyCapsule_CheckExact)
    capsule(PyObject *obj, bool borrowed) : object(obj, borrowed) { }
    explicit capsule(const void *value, void (*destruct)(PyObject *) = nullptr)
        : object(PyCapsule_New(const_cast<void*>(value), nullptr, destruct), false) {
        if (!m_ptr) pybind11_fail("Could not allocate capsule object!");
    }
    template <typename T> operator T *() const {
        T * result = static_cast<T *>(PyCapsule_GetPointer(m_ptr, nullptr));
        if (!result) pybind11_fail("Unable to extract capsule contents!");
        return result;
    }
};

class tuple : public object {
public:
    PYBIND11_OBJECT(tuple, object, PyTuple_Check)
    explicit tuple(size_t size = 0) : object(PyTuple_New((ssize_t) size), false) {
        if (!m_ptr) pybind11_fail("Could not allocate tuple object!");
    }
    size_t size() const { return (size_t) PyTuple_Size(m_ptr); }
    detail::tuple_accessor operator[](size_t index) const { return {*this, index}; }
};

class dict : public object {
public:
    PYBIND11_OBJECT(dict, object, PyDict_Check)
    dict() : object(PyDict_New(), false) {
        if (!m_ptr) pybind11_fail("Could not allocate dict object!");
    }
    template <typename... Args,
              typename = detail::enable_if_t<detail::all_of_t<detail::is_keyword_or_ds, Args...>::value>,
              // MSVC workaround: it can't compile an out-of-line definition, so defer the collector
              typename collector = detail::deferred_t<detail::unpacking_collector<>, Args...>>
    explicit dict(Args &&...args) : dict(collector(std::forward<Args>(args)...).kwargs()) { }

    size_t size() const { return (size_t) PyDict_Size(m_ptr); }
    detail::dict_iterator begin() const { return (++detail::dict_iterator(*this, 0)); }
    detail::dict_iterator end() const { return detail::dict_iterator(); }
    void clear() const { PyDict_Clear(ptr()); }
    bool contains(handle key) const { return PyDict_Contains(ptr(), key.ptr()) == 1; }
    bool contains(const char *key) const { return PyDict_Contains(ptr(), pybind11::str(key).ptr()) == 1; }
};

class sequence : public object {
public:
    PYBIND11_OBJECT(sequence, object, PySequence_Check)
    size_t size() const { return (size_t) PySequence_Size(m_ptr); }
    detail::sequence_accessor operator[](size_t index) const { return {*this, index}; }
};

class list : public object {
public:
    PYBIND11_OBJECT(list, object, PyList_Check)
    explicit list(size_t size = 0) : object(PyList_New((ssize_t) size), false) {
        if (!m_ptr) pybind11_fail("Could not allocate list object!");
    }
    size_t size() const { return (size_t) PyList_Size(m_ptr); }
    detail::list_accessor operator[](size_t index) const { return {*this, index}; }
    void append(handle h) const { PyList_Append(m_ptr, h.ptr()); }
};

class args : public tuple { PYBIND11_OBJECT_DEFAULT(args, tuple, PyTuple_Check) };
class kwargs : public dict { PYBIND11_OBJECT_DEFAULT(kwargs, dict, PyDict_Check)  };

class set : public object {
public:
    PYBIND11_OBJECT(set, object, PySet_Check)
    set() : object(PySet_New(nullptr), false) {
        if (!m_ptr) pybind11_fail("Could not allocate set object!");
    }
    size_t size() const { return (size_t) PySet_Size(m_ptr); }
    bool add(const object &object) const { return PySet_Add(m_ptr, object.ptr()) == 0; }
    void clear() const { PySet_Clear(m_ptr); }
};

class function : public object {
public:
    PYBIND11_OBJECT_DEFAULT(function, object, PyCallable_Check)
    bool is_cpp_function() const {
        handle fun = detail::get_function(m_ptr);
        return fun && PyCFunction_Check(fun.ptr());
    }
};

class buffer : public object {
public:
    PYBIND11_OBJECT_DEFAULT(buffer, object, PyObject_CheckBuffer)

    buffer_info request(bool writable = false) {
        int flags = PyBUF_STRIDES | PyBUF_FORMAT;
        if (writable) flags |= PyBUF_WRITABLE;
        Py_buffer *view = new Py_buffer();
        if (PyObject_GetBuffer(m_ptr, view, flags) != 0)
            throw error_already_set();
        return buffer_info(view);
    }
};

class memoryview : public object {
public:
    explicit memoryview(const buffer_info& info) {
        static Py_buffer buf { };
        // Py_buffer uses signed sizes, strides and shape!..
        static std::vector<Py_ssize_t> py_strides { };
        static std::vector<Py_ssize_t> py_shape { };
        buf.buf = info.ptr;
        buf.itemsize = (Py_ssize_t) info.itemsize;
        buf.format = const_cast<char *>(info.format.c_str());
        buf.ndim = (int) info.ndim;
        buf.len = (Py_ssize_t) info.size;
        py_strides.clear();
        py_shape.clear();
        for (size_t i = 0; i < info.ndim; ++i) {
            py_strides.push_back((Py_ssize_t) info.strides[i]);
            py_shape.push_back((Py_ssize_t) info.shape[i]);
        }
        buf.strides = py_strides.data();
        buf.shape = py_shape.data();
        buf.suboffsets = nullptr;
        buf.readonly = false;
        buf.internal = nullptr;

        m_ptr = PyMemoryView_FromBuffer(&buf);
        if (!m_ptr)
            pybind11_fail("Unable to create memoryview from buffer descriptor");
    }

    PYBIND11_OBJECT_DEFAULT(memoryview, object, PyMemoryView_Check)
};

inline size_t len(handle h) {
    ssize_t result = PyObject_Length(h.ptr());
    if (result < 0)
        pybind11_fail("Unable to compute length of object");
    return (size_t) result;
}

NAMESPACE_BEGIN(detail)
template <typename D> iterator object_api<D>::begin() const { return {PyObject_GetIter(derived().ptr()), false}; }
template <typename D> iterator object_api<D>::end() const { return {nullptr, false}; }
template <typename D> item_accessor object_api<D>::operator[](handle key) const { return {derived(), object(key, true)}; }
template <typename D> item_accessor object_api<D>::operator[](const char *key) const { return {derived(), pybind11::str(key)}; }
template <typename D> obj_attr_accessor object_api<D>::attr(handle key) const { return {derived(), object(key, true)}; }
template <typename D> str_attr_accessor object_api<D>::attr(const char *key) const { return {derived(), key}; }
template <typename D> args_proxy object_api<D>::operator*() const { return args_proxy(derived().ptr()); }
template <typename D> template <typename T> bool object_api<D>::contains(T &&key) const {
    return attr("__contains__")(std::forward<T>(key)).template cast<bool>();
}

template <typename D>
pybind11::str object_api<D>::str() const {
    PyObject *str_value = PyObject_Str(derived().ptr());
#if PY_MAJOR_VERSION < 3
    PyObject *unicode = PyUnicode_FromEncodedObject(str_value, "utf-8", nullptr);
    Py_XDECREF(str_value); str_value = unicode;
#endif
    return {str_value, false};
}

template <typename D>
pybind11::str object_api<D>::repr() const {
    PyObject *str_value = PyObject_Repr(derived().ptr());
#if PY_MAJOR_VERSION < 3
    PyObject *unicode = PyUnicode_FromEncodedObject(str_value, "utf-8", nullptr);
    Py_XDECREF(str_value); str_value = unicode;
#endif
    return {str_value, false};
}

template <typename D>
handle object_api<D>::get_type() const { return (PyObject *) Py_TYPE(derived().ptr()); }

NAMESPACE_END(detail)
NAMESPACE_END(pybind11)