[section boost/python/class.hpp] [section Introduction] `` defines the interface through which users expose their C++ classes to Python. It declares the `class_` class template, which is parameterized on the class type being exposed. It also exposes the `init`, `optional` and `bases` utility class templates, which are used in conjunction with `class_`. `` contains a forward declaration of the `class_` class template. [endsect] [section Class template `class_`] Creates a Python class associated with the C++ type passed as its first parameter. Although it has four template parameters, only the first one is required. The three optional arguments can actually be supplied *in any order*\ ; Boost.Python determines the role of the argument from its type. [table [[Template Parameter][Requirements][Semantics][Default]] [[`T`][A class type.][The class being wrapped][]] [[Bases] [A specialization of [link high_level_components.boost_python_class_hpp.class_template_bases_t1_t2_tn bases<...>] which specifies previously-exposed C++ base classes of `T`.] [Registers `from_python` conversions from wrapped `T` instances to each of its exposed direct and indirect bases. For each polymorphic base `B`, registers conversions from indirectly-held wrapped `B` instances to `T`.][[link high_level_components.boost_python_class_hpp.class_template_bases_t1_t2_tn bases<>]]] [[HeldType][Must be `T`, a class derived from `T`, or a [link concepts.dereferenceable.concept_requirements Dereferenceable] type for which `pointee::type` is `T` or a class derived from `T`.][Specifies the type that is actually embedded in a Python object wrapping a `T` instance when `T`\ 's constructor is called or when a `T` or `T*` is converted to Python without the use of [link function_invocation_and_creation.boost_python_ptr_hpp.functions ptr], `ref`, or [link concepts.callpolicies Call Policies] such as [link function_invocation_and_creation.models_of_callpolicies.boost_python_return_internal_ref.class_template_return_internal_r return_internal_reference]. More details below.][`T`]] [[NonCopyable][If supplied, must be `boost::noncopyable`.][Suppresses automatic registration of `to_python` conversions which copy `T` instances. Required when `T` has no publicly-accessible copy constructor.][An unspecified type other than boost::noncopyable.]] ] [section HeldType Semantics] # If HeldType is derived from `T`, its exposed constructor(s) must accept an initial `PyObject*` argument which refers back to the Python object that contains the HeldType instance, as shown in this example. This argument is not included in the [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] passed to [link high_level_components.boost_python_class_hpp.class_template_class_t_bases_hel.class_template_class_modifier_fu def(init_expr)], below, nor is it passed explicitly by users when Python instances of `T` are created. This idiom allows C++ virtual functions which will be overridden in Python to access the Python object so the Python method can be invoked. Boost.Python automatically registers additional converters which allow wrapped instances of `T` to be passed to wrapped C++ functions expecting HeldType arguments. # Because Boost.Python will always allow wrapped instances of `T` to be passed in place of HeldType arguments, specifying a smart pointer for HeldType allows users to pass Python `T` instances where a smart pointer-to-T is expected. Smart pointers such as `std::auto_ptr<>` or `boost::shared_ptr<>` which contain a nested type `element_type` designating the referent type are automatically supported; additional smart pointer types can be supported by specializing `pointee`. # As in case 1 above, when HeldType is a smart pointer to a class derived from `T`, the initial `PyObject*` argument must be supplied by all of HeldType's exposed constructors. # Except in cases 1 and 3, users may optionally specify that T itself gets initialized with a similar initial `PyObject*` argument by specializing [link utility_and_infrastructure.boost_python_has_back_reference_.class_template_has_back_referenc has_back_reference]. [endsect] [section Class template `class_` synopsis] `` namespace boost { namespace python { template , class HeldType = T , class NonCopyable = unspecified > class class_ : public object { // Constructors with default __init__ class_(char const* name); class_(char const* name, char const* docstring); // Constructors, specifying non-default __init__ template class_(char const* name, Init); template class_(char const* name, char const* docstring, Init); // Exposing additional __init__ functions template class_& def(Init); // defining methods template class_& def(char const* name, F f); template class_& def(char const* name, Fn fn, A1 const&); template class_& def(char const* name, Fn fn, A1 const&, A2 const&); template class_& def(char const* name, Fn fn, A1 const&, A2 const&, A3 const&); // declaring method as static class_& staticmethod(char const* name); // exposing operators template class_& def(detail::operator_); // Raw attribute modification template class_& setattr(char const* name, U const&); // exposing data members template class_& def_readonly(char const* name, D T::*pm); template class_& def_readwrite(char const* name, D T::*pm); // exposing static data members template class_& def_readonly(char const* name, D const& d); template class_& def_readwrite(char const* name, D& d); // property creation template void add_property(char const* name, Get const& fget, char const* doc=0); template void add_property( char const* name, Get const& fget, Set const& fset, char const* doc=0); template void add_static_property(char const* name, Get const& fget); template void add_static_property(char const* name, Get const& fget, Set const& fset); // pickle support template self& def_pickle(PickleSuite const&); self& enable_pickling(); }; }} `` [endsect] [section Class template `class_` constructors] `` class_(char const* name); class_(char const* name, char const* docstring); template class_(char const* name, Init init_spec); template class_(char const* name, char const* docstring, Init init_spec); `` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules]. If docstring is supplied, it must be an [link ntbs]. If `init_spec` is supplied, it must be either the special enumeration constant `no_init` or an [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] compatible with `T`.]] [[Effects][Constructs a `class_` object holding a Boost.Python extension class named name. The named attribute of the [link high_level_components.boost_python_scope_hpp.introduction current scope] is bound to the new extension class. * If supplied, the value of docstring is bound to the `__doc__` attribute of the extension class. * If `init_spec` is `no_init`, a special `__init__` function is generated which always raises a Python exception. Otherwise, `this->def(init_spec)` is called. * If `init_spec` is not supplied, `this->def(init<>())` is called.]] [[Rationale][Allowing the user to specify constructor arguments in the `class_<>` constructor helps her to avoid the common run-time errors which result from invoking wrapped member functions without having exposed an `__init__` function which creates the requisite `T` instance. Types which are not default-constructible will cause a compile-time error unless `Init` is supplied. The user must always supply name as there is currently no portable method to derive the text of the class name from its type.]] ] [endsect] [section Class template `class_` modifier functions] `` template class_& def(Init init_expr); `` [variablelist [[Requires][`init_expr` is the result of an [link high_level_components.boost_python_init_hpp.introduction.init_expressions init-expression] compatible with `T`.]] [[Effects][For each [link high_level_components.boost_python_init_hpp.introduction.init_expressions valid prefix] `P` of `Init`, adds an `__init__(...)` function overload to the extension class accepting P as arguments. Each overload generated constructs an object of HeldType according to the semantics described above, using a copy of init_expr's call policies. If the longest [link high_level_components.boost_python_init_hpp.introduction.init_expressions valid prefix] of Init contains N types and init_expr holds M keywords, an initial sequence of the keywords are used for all but the first N - M arguments of each overload.]] [[Returns][`*this`]] [[Rationale][Allows users to easily expose a class' constructor to Python.]] ] `` template class_& def(char const* name, Fn fn); template class_& def(char const* name, Fn fn, A1 const& a1); template class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2); template class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2, A3 const& a3); `` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules]. * If a1 is the result of an [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions overload-dispatch-expression], only the second form is allowed and fn must be a pointer to function or pointer to member function whose [link arity] is the same as A1's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions maximum arity]. [*Effects:] For each prefix `P` of `Fn`\ 's sequence of argument types, beginning with the one whose length is `A1`\ 's [link function_invocation_and_creation.boost_python_overloads_hpp.introduction.overload_dispatch_expressions minimum arity], adds a `name(...)` method overload to the extension class. Each overload generated invokes a1's call-expression with `P`, using a copy of a1's call policies. If the longest valid prefix of `A1` contains `N` types and a1 holds `M` keywords, an initial sequence of the keywords are used for all but the first `N - M` arguments of each overload. * Otherwise, a single method overload is built around fn, which must not be null: * If fn is a function pointer, its first argument must be of the form U, U cv&, U cv*, or U cv* const&, where T* is convertible to U*, and a1-a3, if supplied, may be selected in any order from the table below. * Otherwise, if fn is a member function pointer, its target must be T or one of its public base classes, and a1-a3, if supplied, may be selected in any order from the table below. * Otherwise, Fn must be [derived from] [link object_wrappers.boost_python_object_hpp.class_object object], and a1-a2, if supplied, may be selcted in any order from the first two rows of the table below. To be useful, fn should be [@http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6 callable]. [table [[Mnemonic Name][Requirements/Type properties][Effects]] [[docstring][Any [link ntbs]][Value will be bound to the __doc__ attribute of the resulting method overload. If an earlier overload supplied a docstring, two newline characters and the new docstring are appended to it.]] [[policies][A model of [link concepts.callpolicies CallPolicies]][A copy will be used as the call policies of the resulting method overload.]] [[keywords][The result of a [link function_invocation_and_creation.boost_python_args_hpp.introduction.keyword_expressions keyword-expression] specifying no more arguments than the [link arity] of fn.][A copy will be used as the call policies of the resulting method overload.]] ] ]] [[Returns][`*this`]] ] ``class_& staticmethod(char const* name);`` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules], and corresponds to a method whose overloads have all been defined.]] [[Effects][Replaces the existing named attribute `x` with the result of invoking `staticmethod(x)` in Python. Specifies that the corresponding method is static and therefore no object instance will be passed to it. This is equivalent to the Python statement:]] ] ``setattr(self, name, staticmethod(getattr(self, name)))`` [variablelist [[Note][Attempting to invoke def(name,...) after invoking staticmethod(name) will [link raise] a RuntimeError.]] [[Returns][`*this`]] ] `` template class_& def(detail::operator_); `` [variablelist [[Effects][Adds a Python [@http://www.python.org/doc/ref/specialnames.html special method] as described [link high_level_components.boost_python_operators_hpp here].]] [[Returns][`*this`]] ] `` template class_& setattr(char const* name, U const& u); `` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]] [[Effects][Converts `u` to Python and adds it to the attribute dictionary of the extension class: ``PyObject_SetAttrString(this->ptr(), name, object(u).ptr());``]] [[Returns][`*this`]] ] `` template void add_property(char const* name, Get const& fget, char const* doc=0); template void add_property( char const* name, Get const& fget, Set const& fset, char const* doc=0); `` [variablelist [[Requires][name is an [link ntbs] which conform to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]] [[Effects][Creates a new Python [@http://www.python.org/2.2.2/descrintro.html#property property] class instance, passing `object(fget)` (and `object(fset)` in the second form) with an (optional) docstring `doc` to its constructor, then adds that property to the Python class object under construction with the given attribute name.]] [[Returns][`*this`]] [[Rationale][Allows users to easily expose functions that can be invoked from Python with attribute access syntax.]] ] `` template void add_static_property(char const* name, Get const& fget); template void add_static_property(char const* name, Get const& fget, Set const& fset); `` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules].]] [[Effects][Creates a Boost.Python.StaticProperty object, passing `object(fget)` (and `object(fset)` in the second form) to its constructor, then adds that property to the Python class under construction with the given attribute name. StaticProperty is a special subclass of Python's property class which can be called without an initial self argument.]] [[Returns][`*this`]] [[Rationale][Allows users to easily expose functions that can be invoked from Python with static attribute access syntax.]] ] `` template class_& def_readonly(char const* name, D T::*pm, char const* doc=0); template class_& def_readonly(char const* name, D const& d); `` [variablelist [[Requires][name is an [link ntbs] which conforms to Python's [@http://www.python.org/doc/current/ref/identifiers.html identifier naming rules]. `doc` is also an [link ntbs].]] [[Effects][``this->add_property(name, make_getter(pm), doc);`` and ``this->add_static_property(name, make_getter(d));`` respectively.]] [[Returns][`*this`]] [[Rationale][Allows users to easily expose a class' data member or free variable such that it can be inspected from Python with a natural syntax.]] ] `` template class_& def_readwrite(char const* name, D T::*pm, char const* doc=0); template class_& def_readwrite(char const* name, D& d); `` [variablelist [[Effects][``this->add_property(name, make_getter(pm), make_setter(pm), doc);`` and ``this->add_static_property(name, make_getter(d), make_setter(d));`` respectively.]] [[Returns][`*this`]] [[Rationale][Allows users to easily expose a class' data or free variable member such that it can be inspected and set from Python with a natural syntax.]] ] `` template class_& def_pickle(PickleSuite const&); `` [variablelist [[Requires][PickleSuite must be publically derived from [link topics.pickle_support.the_pickle_interface pickle_suite].]] [[Effects][Defines a legal combination of the special attributes and methods: __getinitargs__, __getstate__, __setstate__, __getstate_manages_dict__, __safe_for_unpickling__, __reduce__]] [[Returns][`*this`]] [[Rationale][Provides an [link topics.pickle_support.the_pickle_interface easy to use high-level interface] for establishing complete [link topics.pickle_support.the_pickle_interface pickle support] for the wrapped class. The user is protected by compile-time consistency checks.]] ] ``class_& enable_pickling();`` [variablelist [[Effects][Defines the __reduce__ method and the __safe_for_unpickling__ attribute.]] [[Returns][`*this`]] [[Rationale][Light-weight alternative to def_pickle(). Enables implementation of pickle support from Python.]] ] [endsect] [endsect] [section Class template bases] An MPL sequence which can be used in class_<...> instantiations indicate a list of base classes. [section Class template bases synopsis] `` namespace boost { namespace python { template struct bases {}; }} `` [endsect] [endsect] [section Examples] Given a C++ class declaration: `` class Foo : public Bar, public Baz { public: Foo(int x, char const* y); Foo(double); std::string const& name() { return m_name; } void name(char const*); double value; // public data private: ... }; `` A corresponding Boost.Python extension class can be created with: `` using namespace boost::python; class_ >("Foo", "This is Foo's docstring." "It describes our Foo extension class", init(args("x","y"), "__init__ docstring") ) .def(init()) .def("get_name", &Foo::get_name, return_internal_reference<>()) .def("set_name", &Foo::set_name) .def_readwrite("value", &Foo::value); `` [endsect] [endsect]