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Diffstat (limited to '3rdparty/pybind11/docs/advanced/classes.rst')
| -rw-r--r-- | 3rdparty/pybind11/docs/advanced/classes.rst | 213 |
1 files changed, 174 insertions, 39 deletions
diff --git a/3rdparty/pybind11/docs/advanced/classes.rst b/3rdparty/pybind11/docs/advanced/classes.rst index ae5907de..49279020 100644 --- a/3rdparty/pybind11/docs/advanced/classes.rst +++ b/3rdparty/pybind11/docs/advanced/classes.rst @@ -71,7 +71,7 @@ helper class that is defined as follows: /* Trampoline (need one for each virtual function) */ std::string go(int n_times) override { - PYBIND11_OVERLOAD_PURE( + PYBIND11_OVERRIDE_PURE( std::string, /* Return type */ Animal, /* Parent class */ go, /* Name of function in C++ (must match Python name) */ @@ -80,10 +80,10 @@ helper class that is defined as follows: } }; -The macro :c:macro:`PYBIND11_OVERLOAD_PURE` should be used for pure virtual -functions, and :c:macro:`PYBIND11_OVERLOAD` should be used for functions which have -a default implementation. There are also two alternate macros -:c:macro:`PYBIND11_OVERLOAD_PURE_NAME` and :c:macro:`PYBIND11_OVERLOAD_NAME` which +The macro :c:macro:`PYBIND11_OVERRIDE_PURE` should be used for pure virtual +functions, and :c:macro:`PYBIND11_OVERRIDE` should be used for functions which have +a default implementation. There are also two alternate macros +:c:macro:`PYBIND11_OVERRIDE_PURE_NAME` and :c:macro:`PYBIND11_OVERRIDE_NAME` which take a string-valued name argument between the *Parent class* and *Name of the function* slots, which defines the name of function in Python. This is required when the C++ and Python versions of the @@ -122,7 +122,7 @@ Bindings should be made against the actual class, not the trampoline helper clas Note, however, that the above is sufficient for allowing python classes to extend ``Animal``, but not ``Dog``: see :ref:`virtual_and_inheritance` for the -necessary steps required to providing proper overload support for inherited +necessary steps required to providing proper overriding support for inherited classes. The Python session below shows how to override ``Animal::go`` and invoke it via @@ -149,13 +149,17 @@ memory for the C++ portion of the instance will be left uninitialized, which will generally leave the C++ instance in an invalid state and cause undefined behavior if the C++ instance is subsequently used. +.. versionchanged:: 2.6 + The default pybind11 metaclass will throw a ``TypeError`` when it detects + that ``__init__`` was not called by a derived class. + Here is an example: .. code-block:: python class Dachshund(Dog): def __init__(self, name): - Dog.__init__(self) # Without this, undefined behavior may occur if the C++ portions are referenced. + Dog.__init__(self) # Without this, a TypeError is raised. self.name = name def bark(self): return "yap!" @@ -177,15 +181,24 @@ Please take a look at the :ref:`macro_notes` before using this feature. - because in these cases there is no C++ variable to reference (the value is stored in the referenced Python variable), pybind11 provides one in - the PYBIND11_OVERLOAD macros (when needed) with static storage duration. - Note that this means that invoking the overloaded method on *any* + the PYBIND11_OVERRIDE macros (when needed) with static storage duration. + Note that this means that invoking the overridden method on *any* instance will change the referenced value stored in *all* instances of that type. - Attempts to modify a non-const reference will not have the desired effect: it will change only the static cache variable, but this change will not propagate to underlying Python instance, and the change will be - replaced the next time the overload is invoked. + replaced the next time the override is invoked. + +.. warning:: + + The :c:macro:`PYBIND11_OVERRIDE` and accompanying macros used to be called + ``PYBIND11_OVERLOAD`` up until pybind11 v2.5.0, and :func:`get_override` + used to be called ``get_overload``. This naming was corrected and the older + macro and function names may soon be deprecated, in order to reduce + confusion with overloaded functions and methods and ``py::overload_cast`` + (see :ref:`classes`). .. seealso:: @@ -233,20 +246,20 @@ override the ``name()`` method): class PyAnimal : public Animal { public: using Animal::Animal; // Inherit constructors - std::string go(int n_times) override { PYBIND11_OVERLOAD_PURE(std::string, Animal, go, n_times); } - std::string name() override { PYBIND11_OVERLOAD(std::string, Animal, name, ); } + std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, Animal, go, n_times); } + std::string name() override { PYBIND11_OVERRIDE(std::string, Animal, name, ); } }; class PyDog : public Dog { public: using Dog::Dog; // Inherit constructors - std::string go(int n_times) override { PYBIND11_OVERLOAD(std::string, Dog, go, n_times); } - std::string name() override { PYBIND11_OVERLOAD(std::string, Dog, name, ); } - std::string bark() override { PYBIND11_OVERLOAD(std::string, Dog, bark, ); } + std::string go(int n_times) override { PYBIND11_OVERRIDE(std::string, Dog, go, n_times); } + std::string name() override { PYBIND11_OVERRIDE(std::string, Dog, name, ); } + std::string bark() override { PYBIND11_OVERRIDE(std::string, Dog, bark, ); } }; .. note:: - Note the trailing commas in the ``PYBIND11_OVERLOAD`` calls to ``name()`` + Note the trailing commas in the ``PYBIND11_OVERIDE`` calls to ``name()`` and ``bark()``. These are needed to portably implement a trampoline for a function that does not take any arguments. For functions that take a nonzero number of arguments, the trailing comma must be omitted. @@ -261,9 +274,9 @@ declare or override any virtual methods itself: class PyHusky : public Husky { public: using Husky::Husky; // Inherit constructors - std::string go(int n_times) override { PYBIND11_OVERLOAD_PURE(std::string, Husky, go, n_times); } - std::string name() override { PYBIND11_OVERLOAD(std::string, Husky, name, ); } - std::string bark() override { PYBIND11_OVERLOAD(std::string, Husky, bark, ); } + std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, Husky, go, n_times); } + std::string name() override { PYBIND11_OVERRIDE(std::string, Husky, name, ); } + std::string bark() override { PYBIND11_OVERRIDE(std::string, Husky, bark, ); } }; There is, however, a technique that can be used to avoid this duplication @@ -276,15 +289,15 @@ follows: template <class AnimalBase = Animal> class PyAnimal : public AnimalBase { public: using AnimalBase::AnimalBase; // Inherit constructors - std::string go(int n_times) override { PYBIND11_OVERLOAD_PURE(std::string, AnimalBase, go, n_times); } - std::string name() override { PYBIND11_OVERLOAD(std::string, AnimalBase, name, ); } + std::string go(int n_times) override { PYBIND11_OVERRIDE_PURE(std::string, AnimalBase, go, n_times); } + std::string name() override { PYBIND11_OVERRIDE(std::string, AnimalBase, name, ); } }; template <class DogBase = Dog> class PyDog : public PyAnimal<DogBase> { public: using PyAnimal<DogBase>::PyAnimal; // Inherit constructors // Override PyAnimal's pure virtual go() with a non-pure one: - std::string go(int n_times) override { PYBIND11_OVERLOAD(std::string, DogBase, go, n_times); } - std::string bark() override { PYBIND11_OVERLOAD(std::string, DogBase, bark, ); } + std::string go(int n_times) override { PYBIND11_OVERRIDE(std::string, DogBase, go, n_times); } + std::string bark() override { PYBIND11_OVERRIDE(std::string, DogBase, bark, ); } }; This technique has the advantage of requiring just one trampoline method to be @@ -298,8 +311,8 @@ The classes are then registered with pybind11 using: .. code-block:: cpp py::class_<Animal, PyAnimal<>> animal(m, "Animal"); - py::class_<Dog, PyDog<>> dog(m, "Dog"); - py::class_<Husky, PyDog<Husky>> husky(m, "Husky"); + py::class_<Dog, Animal, PyDog<>> dog(m, "Dog"); + py::class_<Husky, Dog, PyDog<Husky>> husky(m, "Husky"); // ... add animal, dog, husky definitions Note that ``Husky`` did not require a dedicated trampoline template class at @@ -337,7 +350,7 @@ valid for the trampoline class but not the registered class. This is primarily for performance reasons: when the trampoline class is not needed for anything except virtual method dispatching, not initializing the trampoline class improves performance by avoiding needing to do a run-time check to see if the -inheriting python instance has an overloaded method. +inheriting python instance has an overridden method. Sometimes, however, it is useful to always initialize a trampoline class as an intermediate class that does more than just handle virtual method dispatching. @@ -368,7 +381,7 @@ references (See also :ref:`faq_reference_arguments`). Another way of solving this is to use the method body of the trampoline class to do conversions to the input and return of the Python method. -The main building block to do so is the :func:`get_overload`, this function +The main building block to do so is the :func:`get_override`, this function allows retrieving a method implemented in Python from within the trampoline's methods. Consider for example a C++ method which has the signature ``bool myMethod(int32_t& value)``, where the return indicates whether @@ -380,10 +393,10 @@ Python side by allowing the Python function to return ``None`` or an ``int``: bool MyClass::myMethod(int32_t& value) { pybind11::gil_scoped_acquire gil; // Acquire the GIL while in this scope. - // Try to look up the overloaded method on the Python side. - pybind11::function overload = pybind11::get_overload(this, "myMethod"); - if (overload) { // method is found - auto obj = overload(value); // Call the Python function. + // Try to look up the overridden method on the Python side. + pybind11::function override = pybind11::get_override(this, "myMethod"); + if (override) { // method is found + auto obj = override(value); // Call the Python function. if (py::isinstance<py::int_>(obj)) { // check if it returned a Python integer type value = obj.cast<int32_t>(); // Cast it and assign it to the value. return true; // Return true; value should be used. @@ -554,6 +567,46 @@ crucial that instances are deallocated on the C++ side to avoid memory leaks. py::class_<MyClass, std::unique_ptr<MyClass, py::nodelete>>(m, "MyClass") .def(py::init<>()) +.. _destructors_that_call_python: + +Destructors that call Python +============================ + +If a Python function is invoked from a C++ destructor, an exception may be thrown +of type :class:`error_already_set`. If this error is thrown out of a class destructor, +``std::terminate()`` will be called, terminating the process. Class destructors +must catch all exceptions of type :class:`error_already_set` to discard the Python +exception using :func:`error_already_set::discard_as_unraisable`. + +Every Python function should be treated as *possibly throwing*. When a Python generator +stops yielding items, Python will throw a ``StopIteration`` exception, which can pass +though C++ destructors if the generator's stack frame holds the last reference to C++ +objects. + +For more information, see :ref:`the documentation on exceptions <unraisable_exceptions>`. + +.. code-block:: cpp + + class MyClass { + public: + ~MyClass() { + try { + py::print("Even printing is dangerous in a destructor"); + py::exec("raise ValueError('This is an unraisable exception')"); + } catch (py::error_already_set &e) { + // error_context should be information about where/why the occurred, + // e.g. use __func__ to get the name of the current function + e.discard_as_unraisable(__func__); + } + } + }; + +.. note:: + + pybind11 does not support C++ destructors marked ``noexcept(false)``. + +.. versionadded:: 2.6 + .. _implicit_conversions: Implicit conversions @@ -768,13 +821,17 @@ An instance can now be pickled as follows: p.setExtra(15) data = pickle.dumps(p, 2) -Note that only the cPickle module is supported on Python 2.7. The second -argument to ``dumps`` is also crucial: it selects the pickle protocol version -2, since the older version 1 is not supported. Newer versions are also fine—for -instance, specify ``-1`` to always use the latest available version. Beware: -failure to follow these instructions will cause important pybind11 memory -allocation routines to be skipped during unpickling, which will likely lead to -memory corruption and/or segmentation faults. + +.. note:: + Note that only the cPickle module is supported on Python 2.7. + + The second argument to ``dumps`` is also crucial: it selects the pickle + protocol version 2, since the older version 1 is not supported. Newer + versions are also fine—for instance, specify ``-1`` to always use the + latest available version. Beware: failure to follow these instructions + will cause important pybind11 memory allocation routines to be skipped + during unpickling, which will likely lead to memory corruption and/or + segmentation faults. .. seealso:: @@ -784,6 +841,38 @@ memory corruption and/or segmentation faults. .. [#f3] http://docs.python.org/3/library/pickle.html#pickling-class-instances +Deepcopy support +================ + +Python normally uses references in assignments. Sometimes a real copy is needed +to prevent changing all copies. The ``copy`` module [#f5]_ provides these +capabilities. + +On Python 3, a class with pickle support is automatically also (deep)copy +compatible. However, performance can be improved by adding custom +``__copy__`` and ``__deepcopy__`` methods. With Python 2.7, these custom methods +are mandatory for (deep)copy compatibility, because pybind11 only supports +cPickle. + +For simple classes (deep)copy can be enabled by using the copy constructor, +which should look as follows: + +.. code-block:: cpp + + py::class_<Copyable>(m, "Copyable") + .def("__copy__", [](const Copyable &self) { + return Copyable(self); + }) + .def("__deepcopy__", [](const Copyable &self, py::dict) { + return Copyable(self); + }, "memo"_a); + +.. note:: + + Dynamic attributes will not be copied in this example. + +.. [#f5] https://docs.python.org/3/library/copy.html + Multiple Inheritance ==================== @@ -1024,7 +1113,7 @@ described trampoline: class Trampoline : public A { public: - int foo() const override { PYBIND11_OVERLOAD(int, A, foo, ); } + int foo() const override { PYBIND11_OVERRIDE(int, A, foo, ); } }; class Publicist : public A { @@ -1042,6 +1131,34 @@ described trampoline: ``.def("foo", static_cast<int (A::*)() const>(&Publicist::foo));`` where ``int (A::*)() const`` is the type of ``A::foo``. +Binding final classes +===================== + +Some classes may not be appropriate to inherit from. In C++11, classes can +use the ``final`` specifier to ensure that a class cannot be inherited from. +The ``py::is_final`` attribute can be used to ensure that Python classes +cannot inherit from a specified type. The underlying C++ type does not need +to be declared final. + +.. code-block:: cpp + + class IsFinal final {}; + + py::class_<IsFinal>(m, "IsFinal", py::is_final()); + +When you try to inherit from such a class in Python, you will now get this +error: + +.. code-block:: pycon + + >>> class PyFinalChild(IsFinal): + ... pass + TypeError: type 'IsFinal' is not an acceptable base type + +.. note:: This attribute is currently ignored on PyPy + +.. versionadded:: 2.6 + Custom automatic downcasters ============================ @@ -1124,3 +1241,21 @@ appropriate derived-class pointer (e.g. using more complete example, including a demonstration of how to provide automatic downcasting for an entire class hierarchy without writing one get() function for each class. + +Accessing the type object +========================= + +You can get the type object from a C++ class that has already been registered using: + +.. code-block:: python + + py::type T_py = py::type::of<T>(); + +You can directly use ``py::type::of(ob)`` to get the type object from any python +object, just like ``type(ob)`` in Python. + +.. note:: + + Other types, like ``py::type::of<int>()``, do not work, see :ref:`type-conversions`. + +.. versionadded:: 2.6 |