Boost.Python

Contents

Introduction

Interface

indexing_suite

indexing_suite sub-classes

vector_indexing_suite

indexing_suite class

vector_indexing_suite class
map_indexing_suite class

Introduction

Indexing is a Boost Python facility for easy exportation of indexable C++ containers to Python. Indexable containers are containers that allow random access through the operator[] (e.g. std::vector).

˷ҽ㨉ndexing㩊ǒ떖Boost Pythonɨʩ㬍 ˼ʇΪK罱㏲Python弳濉˷ҽ儃++ȝƷᣍ 璽㨩ndexable㩈݆奔㬍 Ԋͨ齯perator[]˦뺷IʵĈ݆磨ȧstd::vector㩡㍊

While Boost Python has all the facilities needed to expose indexable C++ containers such as the ubiquitous std::vector to Python, the procedure is not as straightforward as we'd like it to be. Python containers do not map easily to C++ containers. Emulating Python containers in C++ (see Python Reference Manual, Emulating container types) using Boost Python is non trivial. There are a lot of issues to consider before we can map a C++ container to Python. These involve implementing wrapper functions for the methods __len__, __getitem__, __setitem__, __delitem__, __iter__ and __contains.

ˤȻBoost Pythonґߓ뇐ᘒꉨʩ㬍 Ĝ黏␹thon弳濉˷ҽC++ȝƷ 㨀툧Ξ˹⻔ڵijtd::vector㩣썊 嫵쳶齳̲빻첵塣 PythonȝƷ⢲넜ǡ¯ӳɤ彃++ȝƷᣍ ʹӃBoost PythonԚC++֐ģĢPythonȝƷ㨼됹thon⎿슖⡣켡 href= "http://www.python.org/doc/current/ref/sequence-types.html">Emulating container types㩲ⲻ첵塣 ϲPythonӳɤC++ȝƷ֮ǰ㬓ܶΊ̢Ҫ〞ǡ㍊ Ƥ֐ɦ찎꒔ς罷芵ϖ碗ຯʽ㺍 __len__ᢼstrong>__getitem__ᢍ __setitem__ᢼstrong>__delitem__ᢍ __iter__㬺ͼstrong>__containsᣍ

The goals:

Ŀ᪣ꍊ

• Make indexable C++ containers behave exactly as one would expect a Python container to behave.

  ʹ璽儃++ȝƷ儐Ўꍊ ӫPythonȝƷ˹ƚͻ儐Ўꍪȫһւᣍ

• Provide default reference semantics for container element indexing (__getitem__) such that c[i] can be mutable. Require:

  ΪȝƷ儔ꋘ˷ҽ㨼tt>__getitem__㩍 Ĭȏ̡驒퓃ӯҥ㬒Ԋ鼴t>c[i]䡣 Ҫdz㺍

      val = c[i]
      c[i].m()
      val == c[i]
            

  where m is a non-const (mutating) member function (method).

  Ƥ֐mΪ燣onst㨱䶯㩳ɔắʽ㨷���㩡㍊

• Return safe references from __getitem__ such that subsequent adds and deletes to and from the container will not result in dangling references (will not crash Python).

  䓼tt>__getitem__絻ذ∫ҽӃ㬍 բѹ㬒Ժ㶔ȝƷ儌���ꍉ���뻡弖’ҽӃ㨼䲻롊鐹thonက㣩ᣍ

• Support slice indexes.

  ֧㖷ֆ싷ҽ㨳lice index㩡㍊

• Accept Python container arguments (e.g. lists, tuples) wherever appropriate.

  ԚӐ嗥���⎊���ҔʇPythonȝƷ㨈筏stᢴuple㩡㍊

• Allow for extensibility through re-definable policy classes.

  Ԋͨ齒ɖض蒥儲߂Ԁࣨpolicy class㩽萐)չᣍ

• Provide predefined support for the most common STL and STL like indexable containers.

  攓ڗ컵ēTLꍀӔL兒ɋ璽ȝƷ㬍 ̡驔䶨ҥ監糖ᣍ

The Boost.Python Indexing Interface

indexing_suite [ Header <boost/python/indexing/indexing_suite.hpp> ]

The indexing_suite class is the base class for the management of C++ containers intended to be integrated to Python. The objective is make a C++ container look and feel and behave exactly as we'd expect a Python container. The class automatically wraps these special Python methods (taken from the Python reference: Emulating container types):

indexing_suite ʇһ趻造㬍 ӃӚ需퓻쯳ɵ퐹thon儃++ȝƷᣍ ƤĿ᪊ǣ승C++ȝƷ儹۸͐ЎꓫΒC˹ƚ併ĐythonȝƷͪȫһւᣍ 脹ה毷◰բ̘ʢ儐ython罷裨ȡהPython⎿슖⡣꼡 href= "http://www.python.org/doc/current/ref/sequence-types.html">Emulating container types㩣ꍊ

__len__(self)

Called to implement the built-in function len()  Should return the length of the object, an integer >= 0. Also, an object that doesn't define a __nonzero__() method and whose __len__() method returns zero is considered to be false in a Boolean context.  

ִĚփꯊ���t class="function">len()ᣍ Ӧ絻ضԏ㳤戣싼ʇ>= 0 儕늽ᣍ 䋍⣬ȧ黶ԏ㎴樒弴t class= "method">__nonzero__()罷裬 ⢇Ҽtt class= "method">__len__()罷踐똁㣬 Բ膠ԏ㔚⼶뉏ς΄֐Ịӎꦡlseᣍ

__getitem__(self, key)

Called to implement evaluation of self[key]. For sequence types, the accepted keys should be integers and slice objects.  Note that the special interpretation of negative indexes (if the class wishes to emulate a sequence type) is up to the __getitem__() method. If key is of an inappropriate type, TypeError may be raised; if of a value outside the set of indexes for the sequence (after any special interpretation of negative values), IndexError should be raised. Note: for loops expect that an IndexError will be raised for illegal indexes to allow proper detection of the end of the sequence.

ִself[key]dzֵᣍ 攓ڐ⁐ Ѝ㬿ɽӊܵīeyӦ胊Ǖ늽ꍳlice攏㡣 עҢ㬣舧黀ӻģĢP Ѝ㩣썊 攸ꊽ˷ҽ儌؊⽢ʍʇӉ __getitem__()罷踺԰儡㍊ ȧ黼var>keyʇ䭎〠Ѝ㬍 Ԓ���TypeError㻍 ȧ黋璽ֵ㨔ڶԸꖵ팘ʢ���͖㩔���㬍 Ӧ胒���IndexErrorᣍ ע㺼/b> forѭ뷒ꇳ 燷甘ҽŗ㶼tt class= "exception">IndexError㬍 Ҕսȷ쬲␲P���衣

__setitem__(self, key, value)

Called to implement assignment to self[key]. Same note as for __getitem__(). This should only be implemented for mappings if the objects support changes to the values for keys, or if new keys can be added, or for sequences if elements can be replaced. The same exceptions should be raised for improper key values as for the __getitem__() method.

捍code>self[key]賒塣 עҢʂϮӫ__getitem__()Ϡͬᣍ Ӧ能措䋀ӳɤʵϖ㺍 攏㖧㖸츄key˹攓淨ֵ㬍 법߿ɒԌ���Ђ豪ey㬍 법ߐ⁐儔ꋘԱ댦뻡㍊ 攓ڲ땽ȷ儼var>keyֵ㬍 Ӧҽ碓뼴t class= "method">__getitem__()罷荬ѹ儒쳣ᣍ

__delitem__(self, key)

Called to implement deletion of self[key]. Same note as for __getitem__(). This should only be implemented for mappings if the objects support removal of keys, or for sequences if elements can be removed from the sequence. The same exceptions should be raised for improper key values as for the __getitem__() method.

ɾ㽼code>self[key]ᣍ עҢʂϮӫ__getitem__()Ϡͬᣍ Ӧ能措䋀ӳɤʵϖ㺍 攏㖧㖉key㬍 법ߔꋘ뉾㽵Đ⁐ᣍ 攲땽ȷ儼var>key㬍 Ӧҽ碓뼴t class="method">__getitem__()罷菠ͬ儒쳣ᣍ

__iter__(self)

This method is called when an iterator is required for a container. This method should return a new iterator object that can iterate over all the objects in the container. For mappings, it should iterate over the keys of the container, and should also be made available as the method iterkeys().

胸���ԚȝƷҪ弴ꆷʱ巔a㍊ 胸���Ӧ絻ؒ븶Ђ儵촺Ʒ攏㣬 胵촺ƷԱ遠ȝƷ֐˹Ӑ攜ԏ㡣 攓ړ㉤㬋쓦ᩀꈝƷ儼억㬍 ⢇Ғ⿉ͨ齷���iterkeys()̡驡㍊

Iterator objects also need to implement this method; they are required to return themselves. For more information on iterator objects, see ``Iterator Types'' in the Python Library Reference.

弴ꆷ攏㒲Ӑᘒꊵϖ胸���㬍 ˼Cᘐ뷵똋샇הɭᣍ 弴ꆷ攏㵄輶ЅϢ㬇뼻 PythonΒ튖⡼/a> ֐傻 ᰼a class="ulink" href= "http://www.python.org/doc/current/lib/typeiter.html">Iterator Typesᱡ㍊

__contains__(self, item)

Called to implement membership test operators. Should return true if item is in self, false otherwise. For mapping objects, this should consider the keys of the mapping rather than the values or the key-item pairs.

ִ㉔Ტʔ♗硣 ȧitemԚself֐Բ絻ؕ棬籔ⷵ똼١㍊ 攓ړ㉤攏㣬Ӧ胿삇ӳɤ儼죬兗ǖ廲���嶔ᣍ

    class X {...};
    ...

    class_<std::vector<X> >("XVec")
        .def(vector_indexing_suite<std::vector<X> >())
    ;

    class X {...};
    ...

    class_<std::map<X> >("XMap")
        .def(map_indexing_suite<std::map<X> >())
    ;

    template <
          class Container
        , class DerivedPolicies
        , bool NoProxy = false
        , bool NoSlice = false
        , class Data = typename Container::value_type
        , class Index = typename Container::size_type
        , class Key = typename Container::value_type
    >
    class indexing_suite
        : unspecified
    {
    public:

        indexing_suite(); // default constructor
    }
    

        data_type&
        get_item(Container& container, index_type i);

        static object
        get_slice(Container& container, index_type from, index_type to);

        static void
        set_item(Container& container, index_type i, data_type const& v);

        static void
        set_slice(
            Container& container, index_type from,
            index_type to, data_type const& v
        );

        template <class Iter>
        static void
        set_slice(Container& container, index_type from,
            index_type to, Iter first, Iter last
        );

        static void
        delete_item(Container& container, index_type i);

        static void
        delete_slice(Container& container, index_type from, index_type to);

        static size_t
        size(Container& container);

        template <class T>
        static bool
        contains(Container& container, T const& val);

        static index_type
        convert_index(Container& container, PyObject* i);

        static index_type
        adjust_index(index_type current, index_type from,
            index_type to, size_type len
        );

    template <
        class Container,
        bool NoProxy = false,
        class DerivedPolicies = unspecified_default
    class vector_indexing_suite : unspecified_base
    {
    public:

        typedef typename Container::value_type data_type;
        typedef typename Container::value_type key_type;
        typedef typename Container::size_type index_type;
        typedef typename Container::size_type size_type;
        typedef typename Container::difference_type difference_type;
    
        data_type&
        get_item(Container& container, index_type i);

        static object
        get_slice(Container& container, index_type from, index_type to);

        static void
        set_item(Container& container, index_type i, data_type const& v);

        static void
        set_slice(Container& container, index_type from, 
            index_type to, data_type const& v);

        template <class Iter>
        static void
        set_slice(Container& container, index_type from,
            index_type to, Iter first, Iter last);

        static void 
        delete_item(Container& container, index_type i);

        static void 
        delete_slice(Container& container, index_type from, index_type to);
     
        static size_t
        size(Container& container);
     
        static bool
        contains(Container& container, key_type const& key);
     
        static index_type
        convert_index(Container& container, PyObject* i);
     
        static index_type
        adjust_index(index_type current, index_type from, 
            index_type to, size_type len);
    };

    template <
        class Container,
        bool NoProxy = false,
        class DerivedPolicies = unspecified_default
    class map_indexing_suite : unspecified_base
    {
    public:

        typedef typename Container::value_type value_type;
        typedef typename Container::value_type::second_type data_type;
        typedef typename Container::key_type key_type;
        typedef typename Container::key_type index_type;
        typedef typename Container::size_type size_type;
        typedef typename Container::difference_type difference_type;

        static data_type&
        get_item(Container& container, index_type i);

        static void
        set_item(Container& container, index_type i, data_type const& v);

        static void 
        delete_item(Container& container, index_type i);
     
        static size_t
        size(Container& container);
     
        static bool
        contains(Container& container, key_type const& key);
     
        static bool
        compare_index(Container& container, index_type a, index_type b);

        static index_type
        convert_index(Container& container, PyObject* i);
    };