boost/python/init.hpp

Introduction

init-expressions

<boost/python/init.hpp> defines the interface for exposing C++ constructors to Python as extension class __init__ functions.

init-expressions

An init-expression is used to describe a family of __init__ methods to be generated for an extension class, and the result has the following properties:

docstring: An ntbs whose value will bound to the method's __doc__ attribute
keywords: A keyword-expression which will be used to name (a trailing subsequence of) the arguments to the generated __init__ function(s).
call_policies: An instance of a model of CallPolicies.
argument_types: An MPL sequence of C++ argument types which will be used to construct the wrapped C++ object. An init expression has one or more valid prefixes which are given by a sequence of prefixes of its argument types.

Class template `init`

Class template init constructors
Class template init observer functions

A MPL sequence which can be used to specify a family of one or more __init__ functions. Only the last Ti supplied may be an instantiation of optional<...>.

namespace boost { namespace python
{
  template <T1 = unspecified,...Tn = unspecified>
  struct init
  {
    init(char const* doc = 0);
    template <class Keywords> init(Keywords const& kw, char const* doc = 0);
    template <class Keywords> init(char const* doc, Keywords const& kw);

    template <class CallPolicies>
    unspecified operator[](CallPolicies const& policies) const
  };
}}

Class template `init` constructors

init(char const* doc = 0);
template <class Keywords> init(Keywords const& kw, char const* doc = 0);
template <class Keywords> init(char const* doc, Keywords const& kw);

Requires

If supplied, doc is an ntbs. If supplied, kw is the result of a

Effects

The result is an init-expression whose docstring is doc and whose keywords are a reference to kw. If the first form is used, the resulting expression's keywords are empty. The expression's call policies are an instance of default_call_policies. If Tn is optional<U1, U2,... Um>, the expression's valid prefixes are given by:

(T1, T2,...Tn-1), (T1, T2,...Tn-1 , U1), (T1, T2,...Tn-1 , U1, U2), ...(T1, T2,...Tn-1 , U1, U2,...Um)

. Otherwise, the expression has one valid prefix given by the template arguments the user specified.

Class template `init` observer functions

template <class Policies>
unspecified operator[](Policies const& policies) const

Requires: Policies is a model of CallPolicies.
Effects: Returns a new init-expression with all the same properties as the init object except that its call policies are replaced by a reference to policies.

Class template `optional`

A MPL sequence which can be used to specify the optional arguments to an __init__ function.

namespace boost { namespace python
{
  template <T1 = unspecified,...Tn = unspecified>
  struct optional {};
}}

Example

Given the C++ declarations:

class Y;
class X
{
 public:
   X(int x, Y* y) : m_y(y) {}
   X(double);
 private:
   Y* m_y;
};

A corresponing Boost.Python extension class can be created with:

using namespace boost::python;

class_<X>("X", "This is X's docstring.",
          init<int,char const*>(args("x","y"), "X.__init__'s docstring")[
                with_custodian_and_ward<1,3>()]
          )
   .def(init<double>())
   ;