There are a large number of structures which are used in the definition of object types for Python. This section describes these structures and how they are used.
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
and
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. Additional macros can be found under
.
typePyObject
Part of the
. (Only some members are part of the stable ABI.)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
, but every pointer to a Python object can be cast to a
*.
The members must not be accessed directly; instead use macros such as
and
.
ob_refcnt
Part of the
.The object’s reference count, as returned by
. Do not use this field directly; instead use functions and macros such as Py_REFCNT,
and
.
The field type may be different from Py_ssize_t, depending on build configuration and platform.
*ob_type
Part of the
.The object’s type. Do not use this field directly; use
and
instead.
typePyVarObject
Part of the
. (Only some members are part of the stable ABI.)An extension of
that adds the
field. This is intended for objects that have some notion of length.
As with PyObject, the members must not be accessed directly; instead use macros such as
,
and
.
ob_size
Part of the
.A size field, whose contents should be considered an object’s internal implementation detail.
Do not use this field directly; use
instead.
Object creation functions such as
will generally set this field to the requested size (number of items). After creation, arbitrary values can be stored in ob_size using
.
To get an object’s publicly exposed length, as returned by the Python function
, use
instead.
PyObject_HEAD
This is a macro used when declaring new types which represent objects without a varying length. The PyObject_HEAD macro expands to:
PyObjectob_base;See documentation of
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:
PyVarObjectob_base;See documentation of
above.
PyBaseObject_Type
Part of the
.The base class of all other objects, the same as
in Python.
intPy_Is(
*x,
*y)
Part of the
since version 3.10.Test if the x object is the y object, the same as xisy in Python.
Added in version 3.10.
intPy_IsNone(
*x)
Part of the
since version 3.10.Test if an object is the None singleton, the same as xisNone in Python.
Added in version 3.10.
intPy_IsTrue(
*x)
Part of the
since version 3.10.Test if an object is the True singleton, the same as xisTrue in Python.
Added in version 3.10.
intPy_IsFalse(
*x)
Part of the
since version 3.10.Test if an object is the False singleton, the same as xisFalse in Python.
Added in version 3.10.
*Py_TYPE(
*o)
Return value: Borrowed reference. Part of the
since version 3.14.Get the type of the Python object o.
The returned reference is
from o. Do not release it with
or similar.
Changed in version 3.11:
is changed to an inline static function. The parameter type is no longer const
*.
intPy_IS_TYPE(
*o,
*type)
Return non-zero if the object o type is type. Return zero otherwise. Equivalent to: Py_TYPE(o)==type.
Added in version 3.9.
voidPy_SET_TYPE(
*o,
*type)
Set the type of object o to type, without any checking or reference counting.
This is a very low-level operation. Consider instead setting the Python attribute
using
or similar.
Note that assigning an incompatible type can lead to undefined behavior.
If type is a
, the caller must create a new reference to it. Similarly, if the old type of o is a heap type, the caller must release a reference to that type.
Added in version 3.9.
Py_SIZE(
*o)
Get the
field of o.
Changed in version 3.11:
is changed to an inline static function. The parameter type is no longer const
*.
voidPy_SET_SIZE(
*o,
size)
Set the
field of o to size.
Added in version 3.9.
PyObject_HEAD_INIT(type)
This is a macro which expands to initialization values for a new
type. This macro expands to:
_PyObject_EXTRA_INIT1,type,PyVarObject_HEAD_INIT(type, size)
This is a macro which expands to initialization values for a new
type, including the
field. This macro expands to:
_PyObject_EXTRA_INIT1,type,size,Implementing functions and methods
typePyCFunction
Part of the
.Type of the functions used to implement most Python callables in C. Functions of this type take two
* parameters and return one such value. If the return value is NULL, an exception shall have been set. If not NULL, 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);typePyCFunctionWithKeywords
Part of the
.Type of the functions used to implement Python callables in C with signature
. The function signature is:
PyObject*PyCFunctionWithKeywords(PyObject*self,PyObject*args,PyObject*kwargs);typePyCFunctionFast
Part of the
since version 3.13.Type of the functions used to implement Python callables in C with signature
. The function signature is:
PyObject*PyCFunctionFast(PyObject*self,PyObject*const*args,Py_ssize_tnargs);typePyCFunctionFastWithKeywords
Part of the
since version 3.13.Type of the functions used to implement Python callables in C with signature
. The function signature is:
PyObject*PyCFunctionFastWithKeywords(PyObject*self,PyObject*const*args,Py_ssize_tnargs,PyObject*kwnames);typePyCMethod
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_tnargs,PyObject*kwnames)Added in version 3.9.
typePyMethodDef
Part of the
(including all members).Structure used to describe a method of an extension type. This structure has four fields:
constchar*ml_name
Name of the method.
ml_meth
Pointer to the C implementation.
intml_flags
Flags bits indicating how the call should be constructed.
constchar*ml_doc
Points to the contents of the docstring.
The
is a C function pointer. The functions may be of different types, but they always return
*. If the function is not of the
, 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
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
Part of the
.This is the typical calling convention, where the methods have the type
. The function expects two
* 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 using
or
.
METH_KEYWORDS
Can only be used in certain combinations with other flags:
,
and
METH_METHOD | METH_FASTCALL | METH_KEYWORDS
.
|
Methods with these flags must be of type
. The function expects three parameters: self, args, kwargs where kwargs is a dictionary of all the keyword arguments or possibly NULL if there are no keyword arguments. The parameters are typically processed using
.
METH_FASTCALL
Part of the
since version 3.10.Fast calling convention supporting only positional arguments. The methods have the type
. The first parameter is self, the second parameter is a C array of
* values indicating the arguments and the third parameter is the number of arguments (the length of the array).
Added in version 3.7.
Changed in version 3.10: METH_FASTCALL is now part of the
.
|
Extension of
supporting also keyword arguments, with methods of type
. Keyword arguments are passed the same way as in the
: there is an additional fourth
* parameter which is a tuple representing the names of the keyword arguments (which are guaranteed to be strings) or possibly NULL if there are no keywords. The values of the keyword arguments are stored in the args array, after the positional arguments.
Added in version 3.7.
METH_METHOD
Part of the
since version 3.7.Can only be used in the combination with other flags:
METH_METHOD | METH_FASTCALL | METH_KEYWORDS
.
|
|
Extension of
supporting the defining class, that is, the class that contains the method in question. The defining class might be a superclass of Py_TYPE(self).
The method needs to be of type
, the same as for METH_FASTCALL|METH_KEYWORDS with defining_class argument added after self.
Added in version 3.9.
METH_NOARGS
Part of the
.Methods without parameters don’t need to check whether arguments are given if they are listed with the
flag. They need to be of type
. 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 be NULL.
The function must have 2 parameters. Since the second parameter is unused,
can be used to prevent a compiler warning.
METH_O
Part of the
.Methods with a single object argument can be listed with the
flag, instead of invoking
with a "O" argument. They have the type
, with the self parameter, and a
* parameter representing the single argument.
These two constants are not used to indicate the calling convention but the binding when used with methods of classes. These may not be used for functions defined for modules. At most one of these flags may be set for any given method.
METH_CLASS
Part of the
.The method will be passed the type object as the first parameter rather than an instance of the type. This is used to create class methods, similar to what is created when using the
built-in decorator.
METH_STATIC
Part of the
.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 the
built-in decorator.
One other constant controls whether a method is loaded in place of another definition with the same method name.
METH_COEXIST
Part of the
.The method will be loaded in place of existing definitions. Without METH_COEXIST, the default is to skip repeated definitions. Since slot wrappers are loaded before the method table, the existence of a sq_contains slot, for example, would generate a wrapped method named
and preclude the loading of a corresponding PyCFunction with the same name. With the flag defined, the PyCFunction will be loaded in place of the wrapper object and will co-exist with the slot. This is helpful because calls to PyCFunctions are optimized more than wrapper object calls.
PyCMethod_Type
The type object corresponding to Python C method objects. This is available as
in the Python layer.
intPyCMethod_Check(
*op)
Return true if op is an instance of the
type or a subtype of it. This function always succeeds.
intPyCMethod_CheckExact(
*op)
This is the same as
, but does not account for subtypes.
*PyCMethod_New(
*ml,
*self,
*module,
*cls)
Return value: New reference. Part of the
since version 3.9.Turn ml into a Python
object. The caller must ensure that ml outlives the callable. Typically, ml is defined as a static variable.
The self parameter will be passed as the self argument to the C function in ml->ml_meth when invoked. self can be NULL.
The
object’s __module__ attribute can be set from the given module argument. module should be a Python string, which will be used as name of the module the function is defined in. If unavailable, it can be set to
or NULL.
The cls parameter will be passed as the defining_class argument to the C function. Must be set if
is set on ml->ml_flags.
Added in version 3.9.
PyCFunction_Type
Part of the
.The type object corresponding to Python C function objects. This is available as
in the Python layer.
intPyCFunction_Check(
*op)
Return true if op is an instance of the
type or a subtype of it. This function always succeeds.
intPyCFunction_CheckExact(
*op)
This is the same as
, but does not account for subtypes.
*PyCFunction_NewEx(
*ml,
*self,
*module)
Return value: New reference. Part of the
.Equivalent to PyCMethod_New(ml,self,module,NULL).
*PyCFunction_New(
*ml,
*self)
Return value: New reference. Part of the
since version 3.4.Equivalent to PyCMethod_New(ml,self,NULL,NULL).
intPyCFunction_GetFlags(
*func)
Part of the
.Get the function’s flags on func as they were passed to
.
If func is not a C function object, this fails with an exception. func must not be NULL.
This function returns the function’s flags on success, and -1 with an exception set on failure.
intPyCFunction_GET_FLAGS(
*func)
This is the same as
, but without error or type checking.
PyCFunction_GetFunction(
*func)
Part of the
.Get the function pointer on func as it was passed to
.
If func is not a C function object, this fails with an exception. func must not be NULL.
This function returns the function pointer on success, and NULL with an exception set on failure.
intPyCFunction_GET_FUNCTION(
*func)
This is the same as
, but without error or type checking.
*PyCFunction_GetSelf(
*func)
Part of the
.Get the “self” object on func. This is the object that would be passed to the first argument of a
. For C function objects created through a
on a
, this is the resulting module object.
If func is not a C function object, this fails with an exception. func must not be NULL.
This function returns a
to the “self” object on success, and NULL with an exception set on failure.
*PyCFunction_GET_SELF(
*func)
This is the same as
, but without error or type checking.
Accessing attributes of extension types
typePyMemberDef
Part of the
(including all members).Structure which describes an attribute of a type which corresponds to a C struct member. When defining a class, put a NULL-terminated array of these structures in the
slot.
Its fields are, in order:
constchar*name
Name of the member. A NULL value marks the end of a PyMemberDef[] array.
The string should be static, no copy is made of it.
inttype
The type of the member in the C struct. See
for the possible values.
offset
The offset in bytes that the member is located on the type’s object struct.
intflags
Zero or more of the
, combined using bitwise OR.
constchar*doc
The docstring, or NULL. The string should be static, no copy is made of it. Typically, it is defined using
.
By default (when
is 0), members allow both read and write access. Use the
flag for read-only access. Certain types, like
, imply Py_READONLY. Only
(and legacy
) members can be deleted.
For heap-allocated types (created using
or similar), PyMemberDef may contain a definition for the special member "__vectorcalloffset__", corresponding to
in type objects. This member must be defined with Py_T_PYSSIZET, and either Py_READONLY or Py_READONLY|Py_RELATIVE_OFFSET. For example:
staticPyMemberDefspam_type_members[]={{"__vectorcalloffset__",Py_T_PYSSIZET,offsetof(Spam_object,vectorcall),Py_READONLY},{NULL}/* Sentinel */};(You may need to #include<stddef.h> for offsetof().)
The legacy offsets
and
can be defined similarly using "__dictoffset__" and "__weaklistoffset__" members, but extensions are strongly encouraged to use
and
instead.
Changed in version 3.12: PyMemberDef is always available. Previously, it required including "structmember.h".
Changed in version 3.14:
is now allowed for "__vectorcalloffset__", "__dictoffset__" and "__weaklistoffset__".
*PyMember_GetOne(constchar*obj_addr, struct
*m)
Part of the
.Get an attribute belonging to the object at address obj_addr. The attribute is described by PyMemberDefm. Returns NULL on error.
Changed in version 3.12: PyMember_GetOne is always available. Previously, it required including "structmember.h".
intPyMember_SetOne(char*obj_addr, struct
*m,
*o)
Part of the
.Set an attribute belonging to the object at address obj_addr to object o. The attribute to set is described by PyMemberDefm. Returns 0 if successful and a negative value on failure.
Changed in version 3.12: PyMember_SetOne is always available. Previously, it required including "structmember.h".
Member flags
The following flags can be used with
:
Py_READONLY
Part of the
since version 3.12.Not writable.
Py_AUDIT_READ
Part of the
since version 3.12.Emit an object.__getattr__
before reading.
Py_RELATIVE_OFFSET
Part of the
since version 3.12.Indicates that the
of this PyMemberDef entry indicates an offset from the subclass-specific data, rather than from PyObject.
Can only be used as part of the
when creating a class using negative
. It is mandatory in that case. When setting
from the slot during class creation, Python clears the flag and sets
to the offset from the PyObject struct.
Changed in version 3.10: The RESTRICTED, READ_RESTRICTED and WRITE_RESTRICTED macros available with #include"structmember.h" are deprecated. READ_RESTRICTED and RESTRICTED are equivalent to
; WRITE_RESTRICTED does nothing.
Changed in version 3.12: The READONLY macro was renamed to
. The PY_AUDIT_READ macro was renamed with the Py_ prefix. The new names are now always available. Previously, these required #include"structmember.h". The header is still available and it provides the old names.
Member types
can be one of the following macros corresponding to various C types. When the member is accessed in Python, it will be converted to the equivalent Python type. When it is set from Python, it will be converted back to the C type. If that is not possible, an exception such as
or
is raised.
Unless marked (D), attributes defined this way cannot be deleted using e.g.
or
.
Macro name
C type
Python type
Py_T_BYTE
Part of the
since version 3.12.char
Py_T_SHORT
Part of the
since version 3.12.short
Py_T_INT
Part of the
since version 3.12.int
Py_T_LONG
Part of the
since version 3.12.long
Py_T_LONGLONG
Part of the
since version 3.12.longlong
Py_T_UBYTE
Part of the
since version 3.12.unsignedchar
Py_T_UINT
Part of the
since version 3.12.unsignedint
Py_T_USHORT
Part of the
since version 3.12.unsignedshort
Py_T_ULONG
Part of the
since version 3.12.unsignedlong
Py_T_ULONGLONG
Part of the
since version 3.12.unsignedlonglong
Py_T_PYSSIZET
Part of the
since version 3.12.
Py_T_FLOAT
Part of the
since version 3.12.float
Py_T_DOUBLE
Part of the
since version 3.12.double
Py_T_BOOL
Part of the
since version 3.12.char (written as 0 or 1)
Py_T_STRING
Part of the
since version 3.12.constchar* (*)
(RO)
Py_T_STRING_INPLACE
Part of the
since version 3.12.constchar[] (*)
(RO)
Py_T_CHAR
Part of the
since version 3.12.char (0-127)
(**)
Py_T_OBJECT_EX
Part of the
since version 3.12.
*
(D)
(*): Zero-terminated, UTF8-encoded C string. With Py_T_STRING the C representation is a pointer; with Py_T_STRING_INPLACE the string is stored directly in the structure.
(**): String of length 1. Only ASCII is accepted.
(RO): Implies
.
(D): Can be deleted, in which case the pointer is set to NULL. Reading a NULL pointer raises
.
Added in version 3.12: In previous versions, the macros were only available with #include"structmember.h" and were named without the Py_ prefix (e.g. as T_INT). The header is still available and contains the old names, along with the following deprecated types:
T_OBJECT
Like Py_T_OBJECT_EX, but NULL is converted to None. This results in surprising behavior in Python: deleting the attribute effectively sets it to None.
T_NONE
Always None. Must be used with
.
Defining Getters and Setters
typePyGetSetDef
Part of the
(including all members).Structure to define property-like access for a type. See also description of the
slot.
constchar*name
attribute name
get
C function to get the attribute.
set
Optional C function to set or delete the attribute. If NULL, the attribute is read-only.
constchar*doc
optional docstring
void*closure
Optional user data pointer, providing additional data for getter and setter.
typedef
*(*getter)(
*,void*)
Part of the
.The get function takes one
* parameter (the instance) and a user data pointer (the associated closure):
It should return a new reference on success or NULL with a set exception on failure.
typedefint(*setter)(
*,
*,void*)
Part of the
.set functions take two
* parameters (the instance and the value to be set) and a user data pointer (the associated closure):
In case the attribute should be deleted the second parameter is NULL. Should return 0 on success or -1 with a set exception on failure.