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==== Iterators ==== | === C++ Iterators === |
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* Direct exposure of a class' begin() and end() functions: |
* Direct exposure of a class' begin() and end() functions: |
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* Creation of iterators from member functions... | * Creation of iterators from member functions... |
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* ...and member data: | * ...and member data: |
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* The ability to specify boost.python/CallPolicies, e.g. to prevent copying of heavyweight values: | * The ability to specify ["boost.python/CallPolicy"], e.g. to prevent copying of heavyweight values: |
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.def("__iter__", | .def("__iter__" |
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=== Custom Iterators === Suppose we have custom iterator class providing next() member function. To expose it let's take an approach from scitbx package: {{{ inline object pass_through(object const& o) { return o; } template<class Klass, class KlassIter> struct iterator_wrappers { static Klass next(KlassIter& o) { Klass* result = o.next(); if (!result) { PyErr_SetString(PyExc_StopIteration, "No more data."); boost::python::throw_error_already_set(); } return *result; } static void wrap(const char* python_name) { //using namespace boost::python; class_<KlassIter>(python_name, no_init) .def("next", next) .def("__iter__", pass_through) ; } }; BOOST_PYTHON_MODULE(iter) { ... iterator_wrappers<const MyClass,MyIter>().wrap("Iterator"); } }}} |
C++ Iterators
Python iterator support a highly flexible interface allowing:
- Direct exposure of a class' begin() and end() functions:
... .def("__iter__", iterator<list_int>())
- Creation of iterators from member functions...
... .def("__iter__" , range(&my_class::x_begin, &my_class::x_end))
- ...and member data:
... .def("__iter__" , range(&std::pair<char*,char*>::first, &std::pair<char*,char*>::second))
- The ability to specify ["boost.python/CallPolicy"], e.g. to prevent copying of heavyweight values:
... .def("__iter__" , range<return_value_policy<copy_non_const_reference> >( &my_sequence<heavy>::begin , &my_sequence<heavy>::end))
Custom Iterators
Suppose we have custom iterator class providing next() member function. To expose it let's take an approach from scitbx package:
inline object pass_through(object const& o) { return o; } template<class Klass, class KlassIter> struct iterator_wrappers { static Klass next(KlassIter& o) { Klass* result = o.next(); if (!result) { PyErr_SetString(PyExc_StopIteration, "No more data."); boost::python::throw_error_already_set(); } return *result; } static void wrap(const char* python_name) { //using namespace boost::python; class_<KlassIter>(python_name, no_init) .def("next", next) .def("__iter__", pass_through) ; } }; BOOST_PYTHON_MODULE(iter) { ... iterator_wrappers<const MyClass,MyIter>().wrap("Iterator"); }