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Boost.PythonHeaders <boost/python/class.hpp>, <boost/python/class_fwd.hpp> |
class_class_
synopsisclass_
constructorsclass_
modifier functionsbasesbases synopsis<boost/python/class.hpp> 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_.
<boost/python/class_fwd.hpp> contains a forward
declaration of the class_ class template.
class_<T, Bases, HeldType,
NonCopyable>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.
| Template Parameter | Requirements | Semantics | Default |
|---|---|---|---|
T |
A class type. | The class being wrapped | |
Bases |
A specialization of bases<...> which
specifies previously-exposed C++ base classes of T[1]. |
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. |
bases<> |
HeldType |
Must be T, a class derived from T, or a
Dereferenceable type for which
pointee<HeldType>::type
is T or a class derived from T. |
Specifies the type which is actually embedded in a Python object
wrapping a T instance. 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. |
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 init-expression passed to 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.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<HeldType>.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.PyObject* argument
by specializing has_back_reference<T>.class_
synopsis
namespace boost { namespace python
{
template <class T
, class Bases = bases<>
, 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 Init>
class_(char const* name, Init);
template <class Init>
class_(char const* name, char const* docstring, Init);
// Exposing additional __init__ functions
template <class Init>
class_& def(Init);
// defining methods
template <class F>
class_& def(char const* name, F f);
template <class Fn, class A1>
class_& def(char const* name, Fn fn, A1 const&);
template <class Fn, class A1, class A2>
class_& def(char const* name, Fn fn, A1 const&, A2 const&);
template <class Fn, class A1, class A2, class A3>
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 <unspecified>
class_& def(detail::operator_<unspecified>);
// Raw attribute modification
template <class U>
class_& setattr(char const* name, U const&);
// exposing data members
template <class D>
class_& def_readonly(char const* name, D T::*pm);
template <class D>
class_& def_readwrite(char const* name, D T::*pm);
// exposing static data members
template <class D>
class_& def_readonly(char const* name, D const& d);
template <class D>
class_& def_readwrite(char const* name, D& d);
// property creation
template <class Get>
void add_property(char const* name, Get const& fget);
template <class Get, class Set>
void add_property(char const* name, Get const& fget, Set const& fset);
template <class Get>
void add_static_property(char const* name, Get const& fget);
template <class Get, class Set>
void add_static_property(char const* name, Get const& fget, Set const& fset);
// pickle support
template <typename PickleSuite>
self& def_pickle(PickleSuite const&);
self& enable_pickling();
};
}}
class_
constructorsclass_(char const* name); class_(char const* name, char const* docstring); template <class Init> class_(char const* name, Init init_spec); template <class Init> class_(char const* name, char const* docstring, Init init_spec);
name is an ntbs which conforms to Python's identifier
naming rules. If docstring is supplied, it must be an
ntbs. If init_spec is
supplied, it must be either the special enumeration constant
no_init or an init-expression compatible with
T.class_ object holding a
Boost.Python extension class named name. The
named attribute of the current scope is bound to the new
extension class.docstring is bound to
the __doc__ attribute of the extension class.init_spec is no_init, a special
__init__ function is generated which always raises a
Python exception. Otherwise, this->def(init_spec)
is called.init_spec is not supplied,
this->def(init<>()) is called.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.class_ modifier functionstemplate <class Init> class_& def(Init init_expr);
init_expr is the result of an init-expression compatible with
T.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 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.*thistemplate <class F> class_& def(char const* name, Fn fn); template <class Fn, class A1> class_& def(char const* name, Fn fn, A1 const& a1); template <class Fn, class A1, class A2> class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2); template <class Fn, class A1, class A2, class A3> class_& def(char const* name, Fn fn, A1 const& a1, A2 const& a2, A3 const& a3);
name is an ntbs which conforms to Python's identifier
naming rules.a1 is the result of an overload-dispatch-expression,
only the second form is allowed and fn must be a pointer to
function or pointer to member function whose arity is the same as A1's maximum
arity.
Fn's sequence of argument types, beginning with
the one whose length is A1's 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.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.T or one of its public base classes, and
a1-a3, if supplied, may be selected
in any order from the table below.Fn must be [derived from] 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
callable.| Memnonic Name | Requirements/Type properties | Effects |
|---|---|---|
| docstring | Any ntbs. | Value will be bound to the __doc__ attribute
of the resulting method overload. |
| policies | A model of CallPolicies | A copy will be used as the call policies of the resulting method overload. |
| keywords | The result of a keyword-expression
specifying no more arguments than the arity of fn. |
A copy will be used as the call policies of the resulting method overload. |
*thisclass_& staticmethod(char const* name);
name is an ntbs which conforms to Python's identifier
naming rules, and corresponds to a method whose overloads have all
been defined.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)))
def(name,...) after
invoking staticmethod(name) will raise a RuntimeError.*thistemplate <unspecified> class_& def(detail::operator_<unspecified>);
*thistemplate <class U> class_& setattr(char const* name, U const& u);
name is an ntbs which conforms to Python's identifier
naming rules.
PyObject_SetAttrString(this->ptr(), name, object(u).ptr());
*thistemplate <class Get> void add_property(char const* name, Get const& fget); template <class Get, class Set> void add_property(char const* name, Get const& fget, Set const& fset);
name is an ntbs which conforms to Python's identifier
naming rules.property
class instance, passing object(fget) (and object(fset) in the
second form) to its constructor, then adds that property to the Python
class object under construction with the given attribute
name.*thistemplate <class Get> void add_static_property(char const* name, Get const& fget); template <class Get, class Set> void add_static_property(char const* name, Get const& fget, Set const& fset);
name is an ntbs which conforms to Python's identifier
naming rules.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.*thistemplate <class D> class_& def_readonly(char const* name, D T::*pm); template <class D> class_& def_readonly(char const* name, D const& d);
name is an ntbs which conforms to Python's identifier
naming rules.this->add_property(name, make_getter(pm));and
this->add_static_property(name, make_getter(pm));respectively.
*thistemplate <class D> class_& def_readwrite(char const* name, D T::*pm); template <class D> class_& def_readwrite(char const* name, D& d);
this->add_property(name, make_getter(pm), make_setter(pm));and
this->add_static_property(name, make_getter(pm), make_setter(pm));respectively.
*thistemplate <typename PickleSuite> class_& def_pickle(PickleSuite const&);
pickle_suite.__getinitargs__,
__getstate__, __setstate__,
__getstate_manages_dict__,
__safe_for_unpickling__, __reduce__*thisclass_& enable_pickling();
__reduce__ method and
the __safe_for_unpickling__ attribute.
*thisdef_pickle(). Enables implementation of
pickle support from Python.bases<T1, T2,...TN>An MPL sequence
which can be used in class_<...>
instantiations indicate a list of base classes.
bases
synopsis
namespace boost { namespace python
{
template <T1 = unspecified,...Tn = unspecified>
struct bases
{};
}}
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,bases<Bar,Baz> >("Foo",
"This is Foo's docstring."
"It describes our Foo extension class",
init<int,char const*>(args("x","y"), "__init__ docstring")
)
.def(init<double>())
.def("get_name", &Foo::get_name, return_internal_reference<>())
.def("set_name", &Foo::set_name)
.def_readwrite("value", &Foo::value)
;
B in bases, an instance of
class_<B, ...> must have
already been constructed.
class_<Base>("Base");
class_<Derived, bases<Base> >("Derived");
Revised
5 August, 2002
© Copyright Dave Abrahams 2002.