[section boost/python/iterator.hpp]

[section Introduction]

<boost/python/iterator.hpp> provides types and functions for creating [@http://www.python.org/doc/current/lib/typeiter.html Python iterators] from C++ Containers and Iterators. Note that if your `class_` supports random-access iterators, implementing [@http://www.python.org/doc/current/ref/sequence-types.html#l2h-128 __getitem__] (also known as the Sequence Protocol) may serve you better than using this facility: Python will automatically create an iterator type for you (see [@http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-35 `iter()`]), and each access can be range-checked, leaving no possiblity of accessing through an invalidated C++ iterator.

[endsect]

[section Class template `iterator`]

Instances of `iterator<C,P>` hold a reference to a callable Python object which, when invoked from Python, expects a single argument c convertible to C and creates a Python iterator that traverses `[c.begin(), c.end())`. The optional [link concepts.callpolicies CallPolicies] `P` can be used to control how elements are returned during iteration.

In the table below, c is an instance of Container.

[table

[[Template Parameter][Requirements][Semantics][Default]]

[[Container][`[c.begin(),c.end()`) is a valid Iterator range.][The result will convert its argument to c and call c.begin() and c.end() to acquire iterators. To invoke Container's const `begin()` and `end()` functions, make it const.][ ]]

[[NextPolicies][A default-constructible model of [link concepts.callpolicies CallPolicies].][Applied to the resulting iterators' `next()` method.][An unspecified model of [link concepts.callpolicies CallPolicies] which always makes a copy of the result of deferencing the underlying C++ iterator]]

]

``

namespace boost { namespace python

{

template <class Container, class NextPolicies = unspecified>

struct iterator : object

{

iterator();

};

}}

``

[endsect]

[section Class template iterator constructors]

``iterator()``

[variablelist

[[Effects][Initializes its base class with the result of:

``range<NextPolicies>(&iterators<Container>::begin, &iterators<Container>::end)``]]

[[Postconditions][`this->get()` points to a Python callable object which creates a Python iterator as described above.]]

[[Rationale][Provides an easy way to create iterators for the common case where a C++ class being wrapped provides `begin()` and `end()`.]]

]

[endsect]

[section Class template `iterators`]

A utility class template which provides a way to reliably call its argument's `begin()` and `end()` member functions. Note that there is no portable way to take the address of a member function of a C++ standard library container, so `iterators<>` can be particularly helpful when wrapping them.

In the table below, x is an instance of C.

[table

[[Required Valid Expression][Type]]

[[x.begin()][Convertible to C::const_iterator if C is a const type; convertible to C::iterator otherwise.]]

[[x.end()][Convertible to C::const_iterator if C is a const type; convertible to C::iterator otherwise.]]

]

``

namespace boost { namespace python

{

template <class C>

struct iterators

{

typedef typename C::const_iterator iterator;

static iterator begin(C& x);

static iterator end(C& x);

};

}}

``

[endsect]

[section Class template iterators nested types]

If C is a const type,``typedef typename C::const_iterator iterator;``

Otherwise: ``typedef typename C::iterator iterator;``

[endsect]

[section Class template iterators static functions]

``static iterator begin(C&);``

[variablelist [[Returns][`x.begin()`]]]

``static iterator end(C&);``

[variablelist [[Returns][`x.end()`]]]

[endsect]

[section Functions]

``

template <class NextPolicies, class Target, class Accessor1, class Accessor2>

object range(Accessor1 start, Accessor2 finish);

template <class NextPolicies, class Accessor1, class Accessor2>

object range(Accessor1 start, Accessor2 finish);

template <class Accessor1, class Accessor2>

object range(Accessor1 start, Accessor2 finish);

``

[variablelist

[[Requires][ NextPolicies is a default-constructible model of [link concepts.callpolicies CallPolicies].]]

[[Effects][The first form creates a Python callable object which, when invoked, converts its argument to a Target object x, and creates a Python iterator which traverses `[bind(start,_1)(x), bind(finish,_1)(x))`, applying NextPolicies to the iterator's `next()` function.

The second form is identical to the first, except that Target is deduced from Accessor1 as follows:

# If Accessor1 is a function type, Target is the type of its first argument.

# If Accessor1 is a data member pointer of the form `R (T::*)`, Target is identical to `T`.

# If Accessor1 is a member function pointer of the form `R (T::*)(arguments...) cv-opt`, where cv-opt is an optional cv-qualifier, Target is identical to `T`.

The third form is identical to the second, except that NextPolicies is an unspecified model of [link concepts.callpolicies CallPolicies] which always makes a copy of the result of deferencing the underlying C++ iterator

]]

[[Rationale][The use of `boost::bind()` allows C++ iterators to be accessed through functions, member functions or data member pointers. Customization of NextPolicies (e.g. using [link function_invocation_and_creation.models_of_callpolicies.boost_python_return_internal_ref.class_template_return_internal_r return_internal_reference]) is useful when it is expensive to copy sequence elements of a wrapped class type. Customization of Target is useful when Accessor1 is a function object, or when a base class of the intended target type would otherwise be deduced.]]

]

[endsect]

[section Example]

``

#include <boost/python/module.hpp>

#include <boost/python/class.hpp>

#include <vector>

using namespace boost::python;

BOOST_PYTHON_MODULE(demo)

{

class_<std::vector<double> >("dvec")

.def("__iter__", iterator<std::vector<double> >())

;

}

``

[endsect]

[endsect]