Common Object Structures

Base object types and macros

All Python objects ultimately share a small number of fields at the beginning of the object’s representation in memory

• type PyObject: In a normal “release” build, it contains only the object’s reference count and a pointer to the corresponding type object. Access to the members must be done by using the macros Py_REFCNT and Py_TYPE
• type PyVarObject: This is an extension of PyObject that adds the ob_size field. This is only used for objects that have some notion of length.
• PyObject_HEAD: PyObject ob_base;
• PyObject_VAR_HEAD: PyVarObject ob_base;
• int Py_Is(PyObject *x, PyObject *y)
• int Py_IsNone(PyObject *x)
• int Py_IsTrue(PyObject *x)
• int Py_IsFalse(PyObject *x)
• PyTypeObject *Py_TYPE(PyObject *o)
• int Py_IS_TYPE(PyObject *o, PyTypeObject *type)
• void Py_SET_TYPE(PyObject *o, PyTypeObject *type)
• Py_ssize_t Py_REFCNT(PyObject *o)
• void Py_SET_REFCNT(PyObject *o, Py_ssize_t refcnt)
• Py_ssize_t Py_SIZE(PyVarObject *o)
• void Py_SET_SIZE(PyVarObject *o, Py_ssize_t size)
• PyObject_HEAD_INIT(type)
• PyVarObject_HEAD_INIT(type, size)

Implementing functions and methods

• type PyCFunction

PyObject *PyCFunction(PyObject *self,
                      PyObject *args);

• type PyCFunctionWithKeywords

PyObject *PyCFunctionWithKeywords(PyObject *self,
                                  PyObject *args,
                                  PyObject *kwargs);

• type _PyCFunctionFast

PyObject *_PyCFunctionFast(PyObject *self,
                           PyObject *const *args,
                           Py_ssize_t nargs);

• type _PyCFunctionFastWithKeywords

PyObject *_PyCFunctionFastWithKeywords(PyObject *self,
                                       PyObject *const *args,
                                       Py_ssize_t nargs,
                                       PyObject *kwnames);

• type PyCMethod

PyObject *PyCMethod(PyObject *self,
                    PyTypeObject *defining_class,
                    PyObject *const *args,
                    Py_ssize_t nargs,
                    PyObject *kwnames)

• type PyMethodDef
  • const char *ml_name
  • PyCFunction ml_meth
  • int ml_flags
    • METH_VARARGS
    • METH_KEYWORDS
    • METH_VARARGS | METH_KEYWORDS
    • METH_FASTCALL: Fast calling convention supporting only positional arguments
    • METH_FASTCALL | METH_KEYWORDS
    • METH_METHOD
    • METH_METHOD | METH_FASTCALL | METH_KEYWORDS
    • METH_NOARGS
    • METH_O: Methods with a single object argument
    • METH_CLASS: The method will be passed the type object as the first parameter
    • METH_STATIC: The method will be passed NULL as the first parameter
    • METH_COEXIST
  • const char *ml_doc

Accessing attributes of extension types

• type PyMemberDef
  • name
  • type
    • T_INT
    • T_OBJECT: T_OBJECT and T_OBJECT_EX differ in that T_OBJECT returns None if the member is NULL and T_OBJECT_EX raises an AttributeError
    • T_OBJECT_EX
    • T_STRING: interpreted as UTF-8
  • offset
  • flags
  • doc
• PyObject *PyMember_GetOne(const char *obj_addr, struct PyMemberDef *m)
• int PyMember_SetOne(char *obj_addr, struct PyMemberDef *m, PyObject *o)
• type PyGetSetDef
  • name
  • get
  • set
  • doc
  • closure

typedef PyObject *(*getter)(PyObject *, void *);

typedef int (*setter)(PyObject *, PyObject *, void *);