Wspólne struktury obiektów¶
Istnieje duża liczba struktur, które są używane przy definiowaniu rodzajów obiektów w Pythonie. Ten rozdział opisuje te struktury i jak są one używane.
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. These are represented by the
PyObject
and PyVarObject
types, which are defined, in turn,
by the expansions of some macros also used, whether directly or indirectly, in
the definition of all other Python objects.
-
PyObject
¶ All object types are extensions of this type. This is a type which contains the information Python needs to treat a pointer to an object as an object. In a normal „release” build, it contains only the object’s reference count and a pointer to the corresponding type object. Nothing is actually declared to be a
PyObject
, but every pointer to a Python object can be cast to aPyObject*
. Access to the members must be done by using the macrosPy_REFCNT
andPy_TYPE
.
-
PyVarObject
¶ This is an extension of
PyObject
that adds theob_size
field. This is only used for objects that have some notion of length. This type does not often appear in the Python/C API. Access to the members must be done by using the macrosPy_REFCNT
,Py_TYPE
, andPy_SIZE
.
-
PyObject_HEAD
¶ This is a macro used when declaring new types which represent objects without a varying length. The PyObject_HEAD macro expands to:
PyObject ob_base;
See documentation of
PyObject
above.
-
PyObject_VAR_HEAD
¶ This is a macro used when declaring new types which represent objects with a length that varies from instance to instance. The PyObject_VAR_HEAD macro expands to:
PyVarObject ob_base;
See documentation of
PyVarObject
above.
-
Py_TYPE
(o)¶ This macro is used to access the
ob_type
member of a Python object. It expands to:(((PyObject*)(o))->ob_type)
-
int
Py_IS_TYPE
(PyObject *o, PyTypeObject *type)¶ Return non-zero if the object o type is type. Return zero otherwise. Equivalent to:
Py_TYPE(o) == type
.Nowe w wersji 3.9.
-
void
Py_SET_TYPE
(PyObject *o, PyTypeObject *type)¶ Set the object o type to type.
Nowe w wersji 3.9.
-
Py_REFCNT
(o)¶ This macro is used to access the
ob_refcnt
member of a Python object. It expands to:(((PyObject*)(o))->ob_refcnt)
-
void
Py_SET_REFCNT
(PyObject *o, Py_ssize_t refcnt)¶ Set the object o reference counter to refcnt.
Nowe w wersji 3.9.
-
Py_SIZE
(o)¶ This macro is used to access the
ob_size
member of a Python object. It expands to:(((PyVarObject*)(o))->ob_size)
-
void
Py_SET_SIZE
(PyVarObject *o, Py_ssize_t size)¶ Set the object o size to size.
Nowe w wersji 3.9.
-
PyObject_HEAD_INIT
(type)¶ This is a macro which expands to initialization values for a new
PyObject
type. This macro expands to:_PyObject_EXTRA_INIT 1, type,
-
PyVarObject_HEAD_INIT
(type, size)¶ This is a macro which expands to initialization values for a new
PyVarObject
type, including theob_size
field. This macro expands to:_PyObject_EXTRA_INIT 1, type, size,
Implementing functions and methods¶
-
PyCFunction
¶ Type of the functions used to implement most Python callables in C. Functions of this type take two
PyObject*
parameters and return one such value. If the return value isNULL
, an exception shall have been set. If notNULL
, the return value is interpreted as the return value of the function as exposed in Python. The function must return a new reference.The function signature is:
PyObject *PyCFunction(PyObject *self, PyObject *args);
-
PyCFunctionWithKeywords
¶ Type of the functions used to implement Python callables in C with signature
METH_VARARGS | METH_KEYWORDS
. The function signature is:PyObject *PyCFunctionWithKeywords(PyObject *self, PyObject *args, PyObject *kwargs);
-
_PyCFunctionFast
¶ Type of the functions used to implement Python callables in C with signature
METH_FASTCALL
. The function signature is:PyObject *_PyCFunctionFast(PyObject *self, PyObject *const *args, Py_ssize_t nargs);
-
_PyCFunctionFastWithKeywords
¶ Type of the functions used to implement Python callables in C with signature
METH_FASTCALL | METH_KEYWORDS
. The function signature is:PyObject *_PyCFunctionFastWithKeywords(PyObject *self, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames);
-
PyCMethod
¶ Type of the functions used to implement Python callables in C with signature
METH_METHOD | METH_FASTCALL | METH_KEYWORDS
. The function signature is:PyObject *PyCMethod(PyObject *self, PyTypeObject *defining_class, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
Nowe w wersji 3.9.
-
PyMethodDef
¶ Structure used to describe a method of an extension type. This structure has four fields:
Field
typ języka C
Znaczenie
ml_name
const char *
name of the method
ml_meth
PyCFunction
pointer to the C implementation
ml_flags
int
flag bits indicating how the call should be constructed
ml_doc
const char *
points to the contents of the docstring
The ml_meth
is a C function pointer. The functions may be of different
types, but they always return PyObject*
. If the function is not of
the PyCFunction
, the compiler will require a cast in the method table.
Even though PyCFunction
defines the first parameter as
PyObject*
, it is common that the method implementation uses the
specific C type of the self object.
The ml_flags
field is a bitfield which can include the following flags.
The individual flags indicate either a calling convention or a binding
convention.
There are these calling conventions:
-
METH_VARARGS
¶ This is the typical calling convention, where the methods have the type
PyCFunction
. The function expects twoPyObject*
values. The first one is the self object for methods; for module functions, it is the module object. The second parameter (often called args) is a tuple object representing all arguments. This parameter is typically processed usingPyArg_ParseTuple()
orPyArg_UnpackTuple()
.
-
METH_VARARGS | METH_KEYWORDS
Methods with these flags must be of type
PyCFunctionWithKeywords
. The function expects three parameters: self, args, kwargs where kwargs is a dictionary of all the keyword arguments or possiblyNULL
if there are no keyword arguments. The parameters are typically processed usingPyArg_ParseTupleAndKeywords()
.
-
METH_FASTCALL
¶ Fast calling convention supporting only positional arguments. The methods have the type
_PyCFunctionFast
. The first parameter is self, the second parameter is a C array ofPyObject*
values indicating the arguments and the third parameter is the number of arguments (the length of the array).This is not part of the limited API.
Nowe w wersji 3.7.
-
METH_FASTCALL | METH_KEYWORDS
Extension of
METH_FASTCALL
supporting also keyword arguments, with methods of type_PyCFunctionFastWithKeywords
. Keyword arguments are passed the same way as in the vectorcall protocol: there is an additional fourthPyObject*
parameter which is a tuple representing the names of the keyword arguments (which are guaranteed to be strings) or possiblyNULL
if there are no keywords. The values of the keyword arguments are stored in the args array, after the positional arguments.This is not part of the limited API.
Nowe w wersji 3.7.
-
METH_METHOD | METH_FASTCALL | METH_KEYWORDS
Extension of
METH_FASTCALL | METH_KEYWORDS
supporting the defining class, that is, the class that contains the method in question. The defining class might be a superclass ofPy_TYPE(self)
.The method needs to be of type
PyCMethod
, the same as forMETH_FASTCALL | METH_KEYWORDS
withdefining_class
argument added afterself
.Nowe w wersji 3.9.
-
METH_NOARGS
¶ Methods without parameters don’t need to check whether arguments are given if they are listed with the
METH_NOARGS
flag. They need to be of typePyCFunction
. The first parameter is typically named self and will hold a reference to the module or object instance. In all cases the second parameter will beNULL
.
-
METH_O
¶ Methods with a single object argument can be listed with the
METH_O
flag, instead of invokingPyArg_ParseTuple()
with a"O"
argument. They have the typePyCFunction
, with the self parameter, and aPyObject*
parameter representing the single argument.
Te dwie stałe nie są używane do zaznaczania konwencji wywoływania, ale wiążą gdy są używane z metodami klas. Nie mogą być one używane dla funkcji określonych dla modułów. Co najwyżej jedna z tych flag może być ustawiona dla dowolnej danej metody.
-
METH_CLASS
¶ Metodzie zostanie przekazany typ obiektu jako pierwszy parametr zamiast instancji tego typu. Jest to używane aby tworzyć metody klasowe, podobnie do tego, co jest tworzone przy użyciu wbudowanej funkcji
classmethod()
.
-
METH_STATIC
¶ The method will be passed
NULL
as the first parameter rather than an instance of the type. This is used to create static methods, similar to what is created when using thestaticmethod()
built-in function.
Jedna pozostała stała kontroluje czy metoda jest ładowana w miejscu innej definicji o tej samej nazwie metody.
-
METH_COEXIST
¶ Metoda zostanie załadowana w miejsce istniejących definicji. Bez METH_COEXIST, domyślnie pomija się powtórzone definicje. Od kiedy opakowania gniazd są ładowane przed tabelą metod, istnienie na przykład gniazda sq_contains generuje opakowaną metodę nazywaną
__contains__()
i zapobiega ładowaniu odpowiadającej funkcji PyCFunction o tej samej nazwie. Ze zdefiniowaną flagą, PyCFunction zostanie załadowana w miejsce obiektu opakowania i będzie współistniała z gniazdem. To jest pomocne ponieważ wywołania PyCFunction są zoptymalizowane bardziej niż odwołania do obiektów opakowań.
Accessing attributes of extension types¶
-
PyMemberDef
¶ Structure which describes an attribute of a type which corresponds to a C struct member. Its fields are:
Field
typ języka C
Znaczenie
name
const char *
name of the member
type
int
the type of the member in the C struct
offset
Py_ssize_t
the offset in bytes that the member is located on the type’s object struct
flags
int
flag bits indicating if the field should be read-only or writable
doc
const char *
points to the contents of the docstring
type
can be one of manyT_
macros corresponding to various C types. When the member is accessed in Python, it will be converted to the equivalent Python type.Macro name
C type
T_SHORT
short
T_INT
int
T_LONG
long
T_FLOAT
typ (float) zmiennoprzecinkowy pojedynczej precyzji
T_DOUBLE
typ (double) zmiennoprzecinkowy podwójnej precyzji
T_STRING
const char *
T_OBJECT
PyObject *
T_OBJECT_EX
PyObject *
T_CHAR
char
T_BYTE
char
T_UBYTE
nieoznaczony typ znakowy
T_UINT
nieoznaczony typ int
T_USHORT
nieoznaczony typ krótki
T_ULONG
nieoznaczony typ długi
T_BOOL
char
T_LONGLONG
long long
T_ULONGLONG
unsigned long long
T_PYSSIZET
Py_ssize_t
T_OBJECT
andT_OBJECT_EX
differ in thatT_OBJECT
returnsNone
if the member isNULL
andT_OBJECT_EX
raises anAttributeError
. Try to useT_OBJECT_EX
overT_OBJECT
becauseT_OBJECT_EX
handles use of thedel
statement on that attribute more correctly thanT_OBJECT
.flags
can be0
for write and read access orREADONLY
for read-only access. UsingT_STRING
fortype
impliesREADONLY
.T_STRING
data is interpreted as UTF-8. OnlyT_OBJECT
andT_OBJECT_EX
members can be deleted. (They are set toNULL
).Heap allocated types (created using
PyType_FromSpec()
or similar),PyMemberDef
may contain definitions for the special members__dictoffset__
,__weaklistoffset__
and__vectorcalloffset__
, corresponding totp_dictoffset
,tp_weaklistoffset
andtp_vectorcall_offset
in type objects. These must be defined withT_PYSSIZET
andREADONLY
, for example:static PyMemberDef spam_type_members[] = { {"__dictoffset__", T_PYSSIZET, offsetof(Spam_object, dict), READONLY}, {NULL} /* Sentinel */ };
-
PyObject*
PyMember_GetOne
(const char *obj_addr, struct PyMemberDef *m)¶ Get an attribute belonging to the object at address obj_addr. The attribute is described by
PyMemberDef
m. ReturnsNULL
on error.
-
int
PyMember_SetOne
(char *obj_addr, struct PyMemberDef *m, PyObject *o)¶ Set an attribute belonging to the object at address obj_addr to object o. The attribute to set is described by
PyMemberDef
m. Returns0
if successful and a negative value on failure.
-
PyGetSetDef
¶ Structure to define property-like access for a type. See also description of the
PyTypeObject.tp_getset
slot.Field
typ języka C
Znaczenie
name
const char *
attribute name
get
getter
C function to get the attribute
set
setter
optional C function to set or delete the attribute, if omitted the attribute is readonly
doc
const char *
optional docstring
closure
void *
optional function pointer, providing additional data for getter and setter
The
get
function takes onePyObject*
parameter (the instance) and a function pointer (the associatedclosure
):typedef PyObject *(*getter)(PyObject *, void *);
It should return a new reference on success or
NULL
with a set exception on failure.set
functions take twoPyObject*
parameters (the instance and the value to be set) and a function pointer (the associatedclosure
):typedef int (*setter)(PyObject *, PyObject *, void *);
In case the attribute should be deleted the second parameter is
NULL
. Should return0
on success or-1
with a set exception on failure.