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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<title>Boost.Python - <boost/python/class.hpp>,
<boost/python/class_fwd.hpp></title>
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../boost.png" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center"><a href="../index.html">Boost.Python</a></h1>
<h2 align="center">Headers <boost/python/class.hpp>,
<boost/python/class_fwd.hpp></h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#class_-spec">Class template
<code>class_</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#class_-spec-synopsis">Class <code>class_</code>
synopsis</a></dt>
<dt><a href="#class_-spec-ctors">Class <code>class_</code>
constructors</a></dt>
<dt><a href="#class_-spec-modifiers">Class <code>class_</code>
modifier functions</a></dt>
</dl>
</dd>
<dt><a href="#bases-spec">Class template <code>bases</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#bases-spec-synopsis">Class template
<code>bases</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction" id="introduction"></a>Introduction</h2>
<p><code><boost/python/class.hpp></code> defines the interface
through which users expose their C++ classes to Python. It declares the
<code>class_</code> class template, which is parameterized on the class
type being exposed. It also exposes the <code>init</code>,
<code>optional</code> and <code>bases</code> utility class templates, which
are used in conjunction with <code>class_</code>.</p>
<p><code><boost/python/class_fwd.hpp></code> contains a forward
declaration of the <code>class_</code> class template.</p>
<h2><a name="classes" id="classes"></a>Classes</h2>
<h3><a name="class_-spec" id="class_-spec"></a>Class template
<code>class_<T, <font color="#007F00">Bases, HeldType,
NonCopyable</font>></code></h3>
<p>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
<font color="#007F00"><b>in any order</b></font>; Boost.Python determines
the role of the argument from its type.<br>
<br></p>
<table border="1" summary="class_ template parameters">
<tr>
<th>Template Parameter</th>
<th>Requirements</th>
<th>Semantics</th>
<th>Default</th>
</tr>
<tr>
<td><code>T</code></td>
<td>A class type.</td>
<td>The class being wrapped</td>
</tr>
<tr>
<td><code><font color="#007F00">Bases</font></code></td>
<td>A specialization of <a href=
"#bases-spec"><code>bases<</code>...<code>></code></a> which
specifies previously-exposed C++ base classes of <code>T</code><a href=
"#footnote_1">[1]</a>.</td>
<td>Registers <code>from_python</code> conversions from wrapped
<code>T</code> instances to each of its exposed direct and indirect
bases. For each polymorphic base <code>B</code>, registers conversions
from indirectly-held wrapped <code>B</code> instances to
<code>T</code>.</td>
<td><code><a href="#bases-spec">bases<></a></code></td>
</tr>
<tr>
<td><code><font color="#007F00">HeldType</font></code></td>
<td>Must be <code>T</code>, a class derived from <code>T</code>, or a
<a href="Dereferenceable.html">Dereferenceable</a> type for which
<code><a href=
"pointee.html#pointee-spec">pointee</a><HeldType>::type</code> is
<code>T</code> or a class derived from <code>T</code>.</td>
<td>Specifies the type that is actually embedded in a Python object
wrapping a <code>T</code> instance when <code>T</code>'s constructor is
called or when a <code>T</code> or <code>T*</code> is converted to
Python without the use of <a href=
"http://www.boost.org/libs/python/doc/v2/callbacks.html#argument_handling">
<code>ptr</code></a>, <a href=
"http://www.boost.org/libs/python/doc/v2/callbacks.html#argument_handling">
<code>ref</code></a>, or <a href="CallPolicies.html">Call Policies</a>
such as <code><a href=
"return_internal_reference.html">return_internal_reference</a></code>.
More details <a href="#HeldType">below</a>.</td>
<td><code>T</code></td>
</tr>
<tr>
<td><code><font color="#007F00">NonCopyable</font></code></td>
<td>If supplied, must be <a href=
"../../../utility/utility.htm#Class_noncopyable">boost::noncopyable</a>.</td>
<td>Suppresses automatic registration of <code>to_python</code>
conversions which copy <code>T</code> instances. Required when
<code>T</code> has no publicly-accessible copy constructor.</td>
<td>An unspecified type other than
<code>boost::noncopyable</code>.</td>
</tr>
</table>
<h4><a name="HeldType" id="HeldType">HeldType Semantics</a></h4>
<ol>
<li>If <code>HeldType</code> is derived from T, its exposed
constructor(s) must accept an initial <code>PyObject*</code> argument
which refers back to the Python object that contains the
<code>HeldType</code> instance, as shown in <a href=
"call_method.html#examples">this example</a>. This argument is not
included in the <em><a href=
"init.html#init-expressions">init-expression</a></em> passed to <a href=
"#class_-spec-modifiers"><code>def(init_expr)</code></a>, below, nor is
it passed explicitly by users when Python instances of <code>T</code> 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 <code>T</code> to be passed to wrapped C++
functions expecting <code>HeldType</code> arguments.</li>
<li>Because Boost.Python will always allow wrapped instances of
<code>T</code> to be passed in place of <code>HeldType</code> arguments,
specifying a smart pointer for <code>HeldType</code> allows users to pass
Python <code>T</code> instances where a smart pointer-to-<code>T</code>
is expected. Smart pointers such as <code>std::auto_ptr<></code> or
<code><a href=
"../../../smart_ptr/shared_ptr.htm">boost::shared_ptr<></a></code>
which contain a nested type <code>element_type</code> designating the
referent type are automatically supported; additional smart pointer types
can be supported by specializing <a href=
"pointee.html#pointee-spec">pointee<HeldType></a>.</li>
<li>As in case 1 above, when <code>HeldType</code> is a smart pointer to
a class derived from <code>T</code>, the initial <code>PyObject*</code>
argument must be supplied by all of <code>HeldType</code>'s exposed
constructors.</li>
<li>Except in cases 1 and 3, users may optionally specify that T itself
gets initialized with a similar initial <code>PyObject*</code> argument
by specializing <a href=
"has_back_reference.html#has_back_reference-spec">has_back_reference<T></a>.</li>
</ol>
<h4><a name="class_-spec-synopsis" id="class_-spec-synopsis"></a>Class
template <code>class_</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template <class T
<font color="#007F00"> , class Bases = bases<>
, class HeldType = T
, class NonCopyable = <i>unspecified</i>
>
</font> class class_ : public <a href="object.html#object-spec">object</a>
{
// 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 <<i>unspecified</i>>
class_& def(<a href=
"operators.html#operator_-spec">detail::operator_</a><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, char const* doc=0);
template <class Get, class Set>
void add_property(
char const* name, Get const& fget, Set const& fset, char const* doc=0);
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();
};
}}
</pre>
<h4><a name="class_-spec-ctors" id="class_-spec-ctors"></a>Class template
<code>class_</code> constructors</h4>
<pre>
class_(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);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>. If <code>docstring</code> is supplied, it must be an
<a href="definitions.html#ntbs">ntbs</a>. If <code>init_spec</code> is
supplied, it must be either the special enumeration constant
<code>no_init</code> or an <a href=
"init.html#init-expressions">init-expression</a> compatible with
<code>T</code>.</dt>
<dt><b>Effects:</b> Constructs a <code>class_</code> object holding a
Boost.Python extension class named <code>name</code>. The
<code>name</code>d attribute of the <a href=
"scope.html#introduction">current scope</a> is bound to the new extension
class.</dt>
<dd>
<ul>
<li>If supplied, the value of <code>docstring</code> is bound to the
<code>__doc__</code> attribute of the extension class.</li>
<li>If <code>init_spec</code> is <code>no_init</code>, a special
<code>__init__</code> function is generated which always raises a
Python exception. Otherwise, <code>this->def(init_spec)</code> is
called.</li>
<li>If <code>init_spec</code> is not supplied,
<code>this->def(init<>())</code> is called.</li>
</ul>
</dd>
<dt><b>Rationale:</b>Allowing the user to specify constructor arguments
in the <code>class_<></code> constructor helps her to avoid the
common run-time errors which result from invoking wrapped member
functions without having exposed an <code>__init__</code> function which
creates the requisite <code>T</code> instance. Types which are not
default-constructible will cause a compile-time error unless
<code>Init</code> is supplied. The user must always supply
<code>name</code> as there is currently no portable method to derive the
text of the class name from its type.</dt>
</dl>
<h4><a name="class_-spec-modifiers" id="class_-spec-modifiers"></a>Class
template <code>class_</code> modifier functions</h4>
<pre>
template <class Init>
class_& def(Init init_expr);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>init_expr</code> is the result of an <a href=
"init.html#init-expressions">init-expression</a> compatible with
<code>T</code>.</dt>
<dt><b>Effects:</b> For each <a href="init.html#init-expressions">valid
prefix</a> <em>P</em> of <code>Init</code>, adds an
<code>__init__(</code>...<code>)</code> function overload to the
extension class accepting <em>P</em> as arguments. Each overload
generated constructs an object of <code>HeldType</code> according to the
semantics described <a href="#HeldType">above</a>, using a copy of
<code>init_expr</code>'s <a href="CallPolicies.html">call policies</a>.
If the longest <a href="init.html#init-expressions">valid prefix</a> of
<code>Init</code> contains <em>N</em> types and <code>init_expr</code>
holds <em>M</em> keywords, an initial sequence of the keywords are used
for all but the first <em>N</em> - <em>M</em> arguments of each
overload.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose a class' constructor
to Python.</dt>
</dl><br>
<pre>
template <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);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dd>
<ul>
<li>If <code>a1</code> is the result of an <a href=
"overloads.html#overload-dispatch-expression"><em>overload-dispatch-expression</em></a>,
only the second form is allowed and fn must be a pointer to function
or pointer to member function whose <a href="definitions.html#arity">
arity</a> is the same as A1's <a href=
"overloads.html#overload-dispatch-expression"><em>maximum
arity</em></a>.
<dl>
<dt><b>Effects:</b> For each prefix <em>P</em> of
<code>Fn</code>'s sequence of argument types, beginning with the
one whose length is <code>A1</code>'s <a href=
"overloads.html#overload-dispatch-expression"><em>minimum
arity</em></a>, adds a
<code><em>name</em>(</code>...<code>)</code> method overload to
the extension class. Each overload generated invokes
<code>a1</code>'s call-expression with <em>P</em>, using a copy
of <code>a1</code>'s <a href="CallPolicies.html">call
policies</a>. If the longest valid prefix of <code>A1</code>
contains <em>N</em> types and <code>a1</code> holds <em>M</em>
keywords, an initial sequence of the keywords are used for all
but the first <em>N</em> - <em>M</em> arguments of each
overload.<br></dt>
</dl>
</li>
<li>Otherwise, a single method overload is built around fn, which
must not be null:
<ul>
<li>If fn is a function pointer, its first argument must be of
the form <code>U</code>, <code>U <em>cv</em>&</code>, <code>U
<em>cv</em>*</code>, or <code>U <em>cv</em>* const&</code>,
where <code>T*</code> is convertible to <code>U*</code>, and
<code>a1</code>-<code>a3</code>, if supplied, may be selected in
any order from the table below.</li>
<li>Otherwise, if fn is a member function pointer, its target
must be <code>T</code> or one of its public base classes, and
<code>a1</code>-<code>a3</code>, if supplied, may be selected in
any order from the table below.</li>
<li>Otherwise, <code>Fn</code> must be [derived from]
<code><a href="object.html#object-spec">object</a></code>, and
<code>a1-a2</code>, if supplied, may be selcted in any order from
the first two rows of the table below. To be useful,
<code>fn</code> should be <a href=
"http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6">
callable</a>.</li>
</ul>
<table border="1" summary="def() optional arguments">
<tr>
<th>Memnonic Name</th>
<th>Requirements/Type properties</th>
<th>Effects</th>
</tr>
<tr>
<td>docstring</td>
<td>Any <a href="definitions.html#ntbs">ntbs</a>.</td>
<td>Value will be bound to the <code>__doc__</code> attribute
of the resulting method overload. If an earlier overload
supplied a docstring, two newline characters and the new
docstring are appended to it.</td>
</tr>
<tr>
<td>policies</td>
<td>A model of <a href=
"CallPolicies.html">CallPolicies</a></td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
<tr>
<td>keywords</td>
<td>The result of a <a href=
"args.html#keyword-expression"><em>keyword-expression</em></a>
specifying no more arguments than the <a href=
"definitions.html#arity">arity</a> of <code>fn</code>.</td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
</table>
</li>
</ul>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<pre>
class_& staticmethod(char const* name);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>, and corresponds to a method whose overloads have all
been defined.</dt>
<dt><b>Effects:</b> Replaces the existing named attribute <i>x</i> with
the result of invoking <code>staticmethod(</code><i>x</i><code>)</code>
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:</dt>
<dd>
<pre>
setattr(self, name, staticmethod(getattr(self, name)))
</pre>
</dd>
<dt><b>Note:</b> Attempting to invoke <code>def(name,...)</code> after
invoking <code>staticmethod(name)</code> will <a href=
"definitions.html#raise">raise</a> a RuntimeError.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl><br>
<pre>
template <<i>unspecified</i>>
class_& def(<a href=
"operators.html#operator_-spec">detail::operator_</a><unspecified>);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Adds a Python <a href=
"http://www.python.org/doc/ref/specialnames.html">special method</a> as
described <a href="operators.html">here</a>.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<pre>
template <class U>
class_& setattr(char const* name, U const& u);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b> Converts u to Python and adds it to the attribute
dictionary of the extension class:</dt>
<dd>
<blockquote>
<code><a href=
"http://www.python.org/doc/current/api/object.html#l2h-166">PyObject_SetAttrString</a>(this->ptr(),
name, <a href=
"object.html#object-spec-ctors">object</a>(u).ptr());</code>
</blockquote>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl><br>
<pre>
template <class Get>
void add_property(char const* name, Get const& fget, char const* doc=0);
template <class Get, class Set>
void add_property(
char const* name, Get const& fget, Set const& fset, char const* doc=0);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conform to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b> Creates a new Python <a href=
"http://www.python.org/2.2.2/descrintro.html#property"><code>property</code></a>
class instance, passing <code><a href=
"object.html#object-spec-ctors">object</a>(fget)</code> (and
<code><a href="object.html#object-spec-ctors">object</a>(fset)</code> in
the second form) with an (optional) docstring <code>doc</code> to its
constructor, then adds that property to the Python class object under
construction with the given attribute <code>name</code>.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose functions that can be
invoked from Python with attribute access syntax.</dt>
</dl><br>
<pre>
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);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b> Creates a Boost.Python.StaticProperty object, passing
<code><a href="object.html#object-spec-ctors">object</a>(fget)</code>
(and <code><a href=
"object.html#object-spec-ctors">object</a>(fset)</code> in the second
form) to its constructor, then adds that property to the Python class
under construction with the given attribute <code>name</code>.
StaticProperty is a special subclass of Python's <a href=
"http://www.python.org/2.2.2/descrintro.html#property"><code>property</code></a>
class which can be called without an initial <code>self</code>
argument.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose functions that can be
invoked from Python with static attribute access syntax.</dt>
</dl><br>
<pre>
template <class D>
class_& def_readonly(char const* name, D T::*pm, char const* doc=0);
template <class D>
class_& def_readonly(char const* name, D const& d);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>. <code>doc</code> is also an ntbs.</dt>
<dt><b>Effects:</b></dt>
<dd>
<pre>
this->add_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(pm), doc);
</pre>and
<pre>
this->add_static_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(d));
</pre>respectively.<br>
<br>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose a class' data member
or free variable such that it can be inspected from Python with a natural
syntax.</dt>
</dl>
<pre>
template <class D>
class_& def_readwrite(char const* name, D T::*pm, char const* doc=0);
template <class D>
class_& def_readwrite(char const* name, D& d);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b></dt>
<dd>
<pre>
this->add_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(pm), <a href=
"data_members.html#make_setter-spec">make_setter</a>(pm), doc);
</pre>and
<pre>
this->add_static_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(d), <a href=
"data_members.html#make_setter-spec">make_setter</a>(d));
</pre>respectively.<br>
<br>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> 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.</dt>
</dl>
<pre>
template <typename PickleSuite>
class_& def_pickle(PickleSuite const&);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> PickleSuite must be publically derived from <a href=
"pickle.html"><code>pickle_suite</code></a>.</dt>
<dt><b>Effects:</b> Defines a legal combination of the special attributes
and methods: <code>__getinitargs__</code>, <code>__getstate__</code>,
<code>__setstate__</code>, <code>__getstate_manages_dict__</code>,
<code>__safe_for_unpickling__</code>, <code>__reduce__</code></dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Provides an <a href="pickle.html">easy to use
high-level interface</a> for establishing complete pickle support for the
wrapped class. The user is protected by compile-time consistency
checks.</dt>
</dl><br>
<pre>
class_& enable_pickling();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Defines the <code>__reduce__</code> method and the
<code>__safe_for_unpickling__</code> attribute.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Light-weight alternative to
<code>def_pickle()</code>. Enables implementation of <a href=
"pickle.html">pickle support</a> from Python.</dt>
</dl><br>
<h3><a name="bases-spec" id="bases-spec"></a>Class template
<code>bases<T1, T2,</code>...<code>TN></code></h3>
<p>An <a href="../../../mpl/doc/refmanual/forward-sequence.html">MPL
sequence</a> which can be used in
<code>class_<</code>...<code>></code> instantiations indicate a list
of base classes.</p>
<h4><a name="bases-spec-synopsis" id="bases-spec-synopsis"></a>Class
template <code>bases</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template <T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>>
struct bases
{};
}}
</pre>
<h2><a name="examples" id="examples"></a>Example(s)</h2>
<p>Given a C++ class declaration:</p>
<pre>
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:
...
};
</pre>A corresponding Boost.Python extension class can be created with:
<pre>
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)
;
</pre>
<hr>
<a name="footnote_1" id="footnote_1">[1]</a> By "previously-exposed" we
mean that the for each <code>B</code> in <code>bases</code>, an instance of
<code>class_<B<font color="#007F00">, ...</font>></code> must have
already been constructed.
<pre>
class_<Base>("Base");
class_<Derived, bases<Base> >("Derived");
</pre>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
1 November, 2005 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>© Copyright <a href="http://www.boost.org/people/dave_abrahams.htm">Dave
Abrahams</a> 2002.</i></p>
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