python是面向对象的解释性语言,然而python是通过C语言实现的,C语言怎么跟面向对象扯上了关系? C语言可以实现面向对象的性质?
原文链接:http://blog.csdn.net/ordeder/article/details/25296307
#define PyObject_HEAD \ _PyObject_HEAD_EXTRA \ Py_ssize_t ob_refcnt; \ struct _typeobject *ob_type;以上宏等价于:
Py_ssize_t ob_refcnt; struct _typeobject *ob_type;参数: ob_refcnt 作为引用计数(类似智能指针的概念),当引用计数为0的时候对象及被销毁。
参数:_typeobject 即 PyTypeObject实现如下:在python中,一切对对象,包括类型也是一种对象。
typedef struct _typeobject { PyObject_VAR_HEAD const char *tp_name; /* For printing, in format "<module>.<name>" */ Py_ssize_t tp_basicsize, tp_itemsize; /* For allocation */ /* Methods to implement standard operations */ destructor tp_dealloc; printfunc tp_print; getattrfunc tp_getattr; setattrfunc tp_setattr; cmpfunc tp_compare; reprfunc tp_repr; /* Method suites for standard classes */ PyNumberMethods *tp_as_number; PySequenceMethods *tp_as_sequence; PyMappingMethods *tp_as_mapping; ... allocfunc tp_alloc; newfunc tp_new; freefunc tp_free; /* Low-level free-memory routine */ inquiry tp_is_gc; /* For PyObject_IS_GC */ PyObject *tp_bases; PyObject *tp_mro; /* method resolution order */ PyObject *tp_cache; PyObject *tp_subclasses; PyObject *tp_weaklist; destructor tp_del; ... } PyTypeObject;
typedef struct _object { PyObject_HEAD } PyObject;
typedef struct { PyObject_HEAD long ob_ival; } PyIntObject;
typedef struct _dictobject PyDictObject; struct _dictobject { PyObject_HEAD Py_ssize_t ma_fill; /* # Active + # Dummy */ ... PyDictEntry *ma_table; ... };通过对比PyIntObject和PyDictObject可得:类PyIntObject和PyDictObject都继承了基类PyObject(PyObject_HEAD)。
PyIntObject和PyDictObject对PyObject_HEAD中的ob_type的赋值是不同的,分别为:
PyTypeObject PyInt_Type = { PyVarObject_HEAD_INIT(&PyType_Type, 0) "int", sizeof(PyIntObject), 0, (destructor)int_dealloc, /* tp_dealloc */ (printfunc)int_print, /* tp_print */ 0, /* tp_getattr */ 0, /* tp_setattr */ (cmpfunc)int_compare, /* tp_compare */ ... int_new, /* tp_new */ (freefunc)int_free, /* tp_free */ };
PyTypeObject PyDict_Type = { PyVarObject_HEAD_INIT(&PyType_Type, 0) "dict", sizeof(PyDictObject), 0, (destructor)dict_dealloc, /* tp_dealloc */ (printfunc)dict_print, /* tp_print */ 0, /* tp_getattr */ 0, /* tp_setattr */ (cmpfunc)dict_compare, /* tp_compare */ ... dict_new, /* tp_new */ PyObject_GC_Del, /* tp_free */ };
PyObject *ppy = &pydictobj;
ppy -> ob_type -> tp_print 即为: pyintobj -> ob_type -> dict_print
总结:多态,通过不同类对ob_type进行初始化,为通用函数接口注册相应的回调函数,即可实现了多态;