Type Object Structures¶

Quick Reference¶

PyTypeObject Definition¶

The structure definition for PyTypeObject can be found in Include/cpython/object.h. For convenience of reference, this repeats the definition found there:

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;
    Py_ssize_t tp_vectorcall_offset;
    getattrfunc tp_getattr;
    setattrfunc tp_setattr;
    PyAsyncMethods *tp_as_async; /* formerly known as tp_compare (Python 2)
                                    or tp_reserved (Python 3) */
    reprfunc tp_repr;

    /* Method suites for standard classes */

    PyNumberMethods *tp_as_number;
    PySequenceMethods *tp_as_sequence;
    PyMappingMethods *tp_as_mapping;

    /* More standard operations (here for binary compatibility) */

    hashfunc tp_hash;
    ternaryfunc tp_call;
    reprfunc tp_str;
    getattrofunc tp_getattro;
    setattrofunc tp_setattro;

    /* Functions to access object as input/output buffer */
    PyBufferProcs *tp_as_buffer;

    /* Flags to define presence of optional/expanded features */
    unsigned long tp_flags;

    const char *tp_doc; /* Documentation string */

    /* Assigned meaning in release 2.0 */
    /* call function for all accessible objects */
    traverseproc tp_traverse;

    /* delete references to contained objects */
    inquiry tp_clear;

    /* Assigned meaning in release 2.1 */
    /* rich comparisons */
    richcmpfunc tp_richcompare;

    /* weak reference enabler */
    Py_ssize_t tp_weaklistoffset;

    /* Iterators */
    getiterfunc tp_iter;
    iternextfunc tp_iternext;

    /* Attribute descriptor and subclassing stuff */
    PyMethodDef *tp_methods;
    PyMemberDef *tp_members;
    PyGetSetDef *tp_getset;
    // Strong reference on a heap type, borrowed reference on a static type
    PyTypeObject *tp_base;
    PyObject *tp_dict;
    descrgetfunc tp_descr_get;
    descrsetfunc tp_descr_set;
    Py_ssize_t tp_dictoffset;
    initproc tp_init;
    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; /* no longer used */
    void *tp_subclasses;  /* for static builtin types this is an index */
    PyObject *tp_weaklist; /* not used for static builtin types */
    destructor tp_del;

    /* Type attribute cache version tag. Added in version 2.6.
     * If zero, the cache is invalid and must be initialized.
     */
    unsigned int tp_version_tag;

    destructor tp_finalize;
    vectorcallfunc tp_vectorcall;

    /* bitset of which type-watchers care about this type */
    unsigned char tp_watched;

    /* Number of tp_version_tag values used.
     * Set to _Py_ATTR_CACHE_UNUSED if the attribute cache is
     * disabled for this type (e.g. due to custom MRO entries).
     * Otherwise, limited to MAX_VERSIONS_PER_CLASS (defined elsewhere).
     */
    uint16_t tp_versions_used;
} PyTypeObject;

PyObject Slots¶

The type object structure extends the PyVarObject structure. The ob_size field is used for dynamic types (created by type_new(), usually called from a class statement). Note that PyType_Type (the metatype) initializes tp_itemsize, which means that its instances (i.e. type objects) must have the ob_size field.

PyObject.ob_refcnt

The type object’s reference count is initialized to 1 by the PyObject_HEAD_INIT macro. Note that for statically allocated type objects, the type’s instances (objects whose ob_type points back to the type) do not count as references. But for dynamically allocated type objects, the instances do count as references.

Inheritance:

This field is not inherited by subtypes.

PyObject.ob_type

This is the type’s type, in other words its metatype. It is initialized by the argument to the PyObject_HEAD_INIT macro, and its value should normally be &PyType_Type. However, for dynamically loadable extension modules that must be usable on Windows (at least), the compiler complains that this is not a valid initializer. Therefore, the convention is to pass NULL to the PyObject_HEAD_INIT macro and to initialize this field explicitly at the start of the module’s initialization function, before doing anything else. This is typically done like this:

Foo_Type.ob_type = &PyType_Type;

This should be done before any instances of the type are created. PyType_Ready() checks if ob_type is NULL, and if so, initializes it to the ob_type field of the base class. PyType_Ready() will not change this field if it is non-zero.

Inheritance:

This field is inherited by subtypes.

PyVarObject Slots¶

PyVarObject.ob_size

For statically allocated type objects, this should be initialized to zero. For dynamically allocated type objects, this field has a special internal meaning.

This field should be accessed using the Py_SIZE() macro.

Inheritance:

This field is not inherited by subtypes.

PyTypeObject Slots¶

Each slot has a section describing inheritance. If PyType_Ready() may set a value when the field is set to NULL then there will also be a “Default” section. (Note that many fields set on PyBaseObject_Type and PyType_Type effectively act as defaults.)

const char *PyTypeObject.tp_name¶

Pointer to a NUL-terminated string containing the name of the type. For types that are accessible as module globals, the string should be the full module name, followed by a dot, followed by the type name; for built-in types, it should be just the type name. If the module is a submodule of a package, the full package name is part of the full module name. For example, a type named T defined in module M in subpackage Q in package P should have the tp_name initializer "P.Q.M.T".

For dynamically allocated type objects, this should just be the type name, and the module name explicitly stored in the type dict as the value for key '__module__'.

For statically allocated type objects, the tp_name field should contain a dot. Everything before the last dot is made accessible as the __module__ attribute, and everything after the last dot is made accessible as the __name__ attribute.

If no dot is present, the entire tp_name field is made accessible as the __name__ attribute, and the __module__ attribute is undefined (unless explicitly set in the dictionary, as explained above). This means your type will be impossible to pickle. Additionally, it will not be listed in module documentations created with pydoc.

This field must not be NULL. It is the only required field in PyTypeObject() (other than potentially tp_itemsize).

Inheritance:

This field is not inherited by subtypes.

Py_ssize_t PyTypeObject.tp_basicsize¶

Py_ssize_t PyTypeObject.tp_itemsize¶

These fields allow calculating the size in bytes of instances of the type.

There are two kinds of types: types with fixed-length instances have a zero tp_itemsize field, types with variable-length instances have a non-zero tp_itemsize field. For a type with fixed-length instances, all instances have the same size, given in tp_basicsize. (Exceptions to this rule can be made using PyUnstable_Object_GC_NewWithExtraData().)

For a type with variable-length instances, the instances must have an ob_size field, and the instance size is tp_basicsize plus N times tp_itemsize, where N is the “length” of the object.

Functions like PyObject_NewVar() will take the value of N as an argument, and store in the instance’s ob_size field. Note that the ob_size field may later be used for other purposes. For example, int instances use the bits of ob_size in an implementation-defined way; the underlying storage and its size should be accessed using PyLong_Export().

Note

The ob_size field should be accessed using the Py_SIZE() and Py_SET_SIZE() macros.

Also, the presence of an ob_size field in the instance layout doesn’t mean that the instance structure is variable-length. For example, the list type has fixed-length instances, yet those instances have a ob_size field. (As with int, avoid reading lists’ ob_size directly. Call PyList_Size() instead.)

The tp_basicsize includes size needed for data of the type’s tp_base, plus any extra data needed by each instance.

The correct way to set tp_basicsize is to use the sizeof operator on the struct used to declare the instance layout. This struct must include the struct used to declare the base type. In other words, tp_basicsize must be greater than or equal to the base’s tp_basicsize.

Since every type is a subtype of object, this struct must include PyObject or PyVarObject (depending on whether ob_size should be included). These are usually defined by the macro PyObject_HEAD or PyObject_VAR_HEAD, respectively.

The basic size does not include the GC header size, as that header is not part of PyObject_HEAD.

For cases where struct used to declare the base type is unknown, see PyType_Spec.basicsize and PyType_FromMetaclass().

Notes about alignment:

• tp_basicsize must be a multiple of _Alignof(PyObject). When using sizeof on a struct that includes PyObject_HEAD, as recommended, the compiler ensures this. When not using a C struct, or when using compiler extensions like __attribute__((packed)), it is up to you.

• If the variable items require a particular alignment, tp_basicsize and tp_itemsize must each be a multiple of that alignment. For example, if a type’s variable part stores a double, it is your responsibility that both fields are a multiple of _Alignof(double).

Inheritance:

These fields are inherited separately by subtypes. (That is, if the field is set to zero, PyType_Ready() will copy the value from the base type, indicating that the instances do not need additional storage.)

If the base type has a non-zero tp_itemsize, it is generally not safe to set tp_itemsize to a different non-zero value in a subtype (though this depends on the implementation of the base type).

destructor PyTypeObject.tp_dealloc¶

The corresponding slot ID Py_tp_dealloc is part of the Stable ABI.

A pointer to the instance destructor function. The function signature is:

void tp_dealloc(PyObject *self);

The destructor function should remove all references which the instance owns (e.g., call Py_CLEAR()), free all memory buffers owned by the instance, and call the type’s tp_free function to free the object itself.

If you may call functions that may set the error indicator, you must use PyErr_GetRaisedException() and PyErr_SetRaisedException() to ensure you don’t clobber a preexisting error indicator (the deallocation could have occurred while processing a different error):

static void
foo_dealloc(foo_object *self)
{
    PyObject *et, *ev, *etb;
    PyObject *exc = PyErr_GetRaisedException();
    ...
    PyErr_SetRaisedException(exc);
}

The dealloc handler itself must not raise an exception; if it hits an error case it should call PyErr_FormatUnraisable() to log (and clear) an unraisable exception.

No guarantees are made about when an object is destroyed, except:

• Python will destroy an object immediately or some time after the final reference to the object is deleted, unless its finalizer (tp_finalize) subsequently resurrects the object.

• An object will not be destroyed while it is being automatically finalized (tp_finalize) or automatically cleared (tp_clear).

CPython currently destroys an object immediately from Py_DECREF() when the new reference count is zero, but this may change in a future version.

It is recommended to call PyObject_CallFinalizerFromDealloc() at the beginning of tp_dealloc to guarantee that the object is always finalized before destruction.

If the type supports garbage collection (the Py_TPFLAGS_HAVE_GC flag is set), the destructor should call PyObject_GC_UnTrack() before clearing any member fields.

It is permissible to call tp_clear from tp_dealloc to reduce code duplication and to guarantee that the object is always cleared before destruction. Beware that tp_clear might have already been called.

If the type is heap allocated (Py_TPFLAGS_HEAPTYPE), the deallocator should release the owned reference to its type object (via Py_DECREF()) after calling the type deallocator. See the example code below.:

static void
foo_dealloc(PyObject *op)
{
   foo_object *self = (foo_object *) op;
   PyObject_GC_UnTrack(self);
   Py_CLEAR(self->ref);
   Py_TYPE(self)->tp_free(self);
}

tp_dealloc must leave the exception status unchanged. If it needs to call something that might raise an exception, the exception state must be backed up first and restored later (after logging any exceptions with PyErr_WriteUnraisable()).

Example:

static void
foo_dealloc(PyObject *self)
{
    PyObject *exc = PyErr_GetRaisedException();

    if (PyObject_CallFinalizerFromDealloc(self) < 0) {
        // self was resurrected.
        goto done;
    }

    PyTypeObject *tp = Py_TYPE(self);

    if (tp->tp_flags & Py_TPFLAGS_HAVE_GC) {
        PyObject_GC_UnTrack(self);
    }

    // Optional, but convenient to avoid code duplication.
    if (tp->tp_clear && tp->tp_clear(self) < 0) {
        PyErr_WriteUnraisable(self);
    }

    // Any additional destruction goes here.

    tp->tp_free(self);
    self = NULL;  // In case PyErr_WriteUnraisable() is called below.

    if (tp->tp_flags & Py_TPFLAGS_HEAPTYPE) {
        Py_CLEAR(tp);
    }

done:
    // Optional, if something was called that might have raised an
    // exception.
    if (PyErr_Occurred()) {
        PyErr_WriteUnraisable(self);
    }
    PyErr_SetRaisedException(exc);
}

tp_dealloc may be called from any Python thread, not just the thread which created the object (if the object becomes part of a refcount cycle, that cycle might be collected by a garbage collection on any thread). This is not a problem for Python API calls, since the thread on which tp_dealloc is called with an attached thread state. However, if the object being destroyed in turn destroys objects from some other C library, care should be taken to ensure that destroying those objects on the thread which called tp_dealloc will not violate any assumptions of the library.

Inheritance:

This field is inherited by subtypes.

See also

Object Life Cycle for details about how this slot relates to other slots.

Py_ssize_t PyTypeObject.tp_vectorcall_offset¶

An optional offset to a per-instance function that implements calling the object using the vectorcall protocol, a more efficient alternative of the simpler tp_call.

This field is only used if the flag Py_TPFLAGS_HAVE_VECTORCALL is set. If so, this must be a positive integer containing the offset in the instance of a vectorcallfunc pointer.

The vectorcallfunc pointer may be NULL, in which case the instance behaves as if Py_TPFLAGS_HAVE_VECTORCALL was not set: calling the instance falls back to tp_call.

Any class that sets Py_TPFLAGS_HAVE_VECTORCALL must also set tp_call and make sure its behaviour is consistent with the vectorcallfunc function. This can be done by setting tp_call to PyVectorcall_Call().

Changed in version 3.8: Before version 3.8, this slot was named tp_print. In Python 2.x, it was used for printing to a file. In Python 3.0 to 3.7, it was unused.

Changed in version 3.12: Before version 3.12, it was not recommended for mutable heap types to implement the vectorcall protocol. When a user sets __call__ in Python code, only tp_call is updated, likely making it inconsistent with the vectorcall function. Since 3.12, setting __call__ will disable vectorcall optimization by clearing the Py_TPFLAGS_HAVE_VECTORCALL flag.

Inheritance:

This field is always inherited. However, the Py_TPFLAGS_HAVE_VECTORCALL flag is not always inherited. If it’s not set, then the subclass won’t use vectorcall, except when PyVectorcall_Call() is explicitly called.

getattrfunc PyTypeObject.tp_getattr¶

The corresponding slot ID Py_tp_getattr is part of the Stable ABI.

An optional pointer to the get-attribute-string function.

This field is deprecated. When it is defined, it should point to a function that acts the same as the tp_getattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: tp_getattr, tp_getattro

This field is inherited by subtypes together with tp_getattro: a subtype inherits both tp_getattr and tp_getattro from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.

setattrfunc PyTypeObject.tp_setattr¶

The corresponding slot ID Py_tp_setattr is part of the Stable ABI.

An optional pointer to the function for setting and deleting attributes.

This field is deprecated. When it is defined, it should point to a function that acts the same as the tp_setattro function, but taking a C string instead of a Python string object to give the attribute name.

Inheritance:

Group: tp_setattr, tp_setattro

This field is inherited by subtypes together with tp_setattro: a subtype inherits both tp_setattr and tp_setattro from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.

PyAsyncMethods *PyTypeObject.tp_as_async¶

Pointer to an additional structure that contains fields relevant only to objects which implement awaitable and asynchronous iterator protocols at the C-level. See Async Object Structures for details.

Added in version 3.5: Formerly known as tp_compare and tp_reserved.

Inheritance:

The tp_as_async field is not inherited, but the contained fields are inherited individually.

reprfunc PyTypeObject.tp_repr¶

The corresponding slot ID Py_tp_repr is part of the Stable ABI.

An optional pointer to a function that implements the built-in function repr().

The signature is the same as for PyObject_Repr():

PyObject *tp_repr(PyObject *self);

The function must return a string or a Unicode object. Ideally, this function should return a string that, when passed to eval(), given a suitable environment, returns an object with the same value. If this is not feasible, it should return a string starting with '<' and ending with '>' from which both the type and the value of the object can be deduced.

Inheritance:

This field is inherited by subtypes.

Default:

When this field is not set, a string of the form <%s object at %p> is returned, where %s is replaced by the type name, and %p by the object’s memory address.

PyNumberMethods *PyTypeObject.tp_as_number¶

Pointer to an additional structure that contains fields relevant only to objects which implement the number protocol. These fields are documented in Number Object Structures.

Inheritance:

The tp_as_number field is not inherited, but the contained fields are inherited individually.

PySequenceMethods *PyTypeObject.tp_as_sequence¶

Pointer to an additional structure that contains fields relevant only to objects which implement the sequence protocol. These fields are documented in Sequence Object Structures.

Inheritance:

The tp_as_sequence field is not inherited, but the contained fields are inherited individually.

PyMappingMethods *PyTypeObject.tp_as_mapping¶

Pointer to an additional structure that contains fields relevant only to objects which implement the mapping protocol. These fields are documented in Mapping Object Structures.

Inheritance:

The tp_as_mapping field is not inherited, but the contained fields are inherited individually.

hashfunc PyTypeObject.tp_hash¶

The corresponding slot ID Py_tp_hash is part of the Stable ABI.

An optional pointer to a function that implements the built-in function hash().

The signature is the same as for PyObject_Hash():

Py_hash_t tp_hash(PyObject *);

The value -1 should not be returned as a normal return value; when an error occurs during the computation of the hash value, the function should set an exception and return -1.

When this field is not set (and tp_richcompare is not set), an attempt to take the hash of the object raises TypeError. This is the same as setting it to PyObject_HashNotImplemented().

This field can be set explicitly to PyObject_HashNotImplemented() to block inheritance of the hash method from a parent type. This is interpreted as the equivalent of __hash__ = None at the Python level, causing isinstance(o, collections.Hashable) to correctly return False. Note that the converse is also true - setting __hash__ = None on a class at the Python level will result in the tp_hash slot being set to PyObject_HashNotImplemented().

Inheritance:

Group: tp_hash, tp_richcompare

This field is inherited by subtypes together with tp_richcompare: a subtype inherits both of tp_richcompare and tp_hash, when the subtype’s tp_richcompare and tp_hash are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericHash().

ternaryfunc PyTypeObject.tp_call¶

The corresponding slot ID Py_tp_call is part of the Stable ABI.

An optional pointer to a function that implements calling the object. This should be NULL if the object is not callable. The signature is the same as for PyObject_Call():

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

Inheritance:

This field is inherited by subtypes.

reprfunc PyTypeObject.tp_str¶

The corresponding slot ID Py_tp_str is part of the Stable ABI.

An optional pointer to a function that implements the built-in operation str(). (Note that str is a type now, and str() calls the constructor for that type. This constructor calls PyObject_Str() to do the actual work, and PyObject_Str() will call this handler.)

The signature is the same as for PyObject_Str():

PyObject *tp_str(PyObject *self);

The function must return a string or a Unicode object. It should be a “friendly” string representation of the object, as this is the representation that will be used, among other things, by the print() function.

Inheritance:

This field is inherited by subtypes.

Default:

When this field is not set, PyObject_Repr() is called to return a string representation.

getattrofunc PyTypeObject.tp_getattro¶

The corresponding slot ID Py_tp_getattro is part of the Stable ABI.

An optional pointer to the get-attribute function.

The signature is the same as for PyObject_GetAttr():

PyObject *tp_getattro(PyObject *self, PyObject *attr);

It is usually convenient to set this field to PyObject_GenericGetAttr(), which implements the normal way of looking for object attributes.

Inheritance:

Group: tp_getattr, tp_getattro

This field is inherited by subtypes together with tp_getattr: a subtype inherits both tp_getattr and tp_getattro from its base type when the subtype’s tp_getattr and tp_getattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericGetAttr().

setattrofunc PyTypeObject.tp_setattro¶

The corresponding slot ID Py_tp_setattro is part of the Stable ABI.

An optional pointer to the function for setting and deleting attributes.

The signature is the same as for PyObject_SetAttr():

int tp_setattro(PyObject *self, PyObject *attr, PyObject *value);

In addition, setting value to NULL to delete an attribute must be supported. It is usually convenient to set this field to PyObject_GenericSetAttr(), which implements the normal way of setting object attributes.

Inheritance:

Group: tp_setattr, tp_setattro

This field is inherited by subtypes together with tp_setattr: a subtype inherits both tp_setattr and tp_setattro from its base type when the subtype’s tp_setattr and tp_setattro are both NULL.

Default:

PyBaseObject_Type uses PyObject_GenericSetAttr().

PyBufferProcs *PyTypeObject.tp_as_buffer¶

Pointer to an additional structure that contains fields relevant only to objects which implement the buffer interface. These fields are documented in Buffer Object Structures.

Inheritance:

The tp_as_buffer field is not inherited, but the contained fields are inherited individually.

unsigned long PyTypeObject.tp_flags¶

This field is a bit mask of various flags. Some flags indicate variant semantics for certain situations; others are used to indicate that certain fields in the type object (or in the extension structures referenced via tp_as_number, tp_as_sequence, tp_as_mapping, and tp_as_buffer) that were historically not always present are valid; if such a flag bit is clear, the type fields it guards must not be accessed and must be considered to have a zero or NULL value instead.

Inheritance:

Inheritance of this field is complicated. Most flag bits are inherited individually, i.e. if the base type has a flag bit set, the subtype inherits this flag bit. The flag bits that pertain to extension structures are strictly inherited if the extension structure is inherited, i.e. the base type’s value of the flag bit is copied into the subtype together with a pointer to the extension structure. The Py_TPFLAGS_HAVE_GC flag bit is inherited together with the tp_traverse and tp_clear fields, i.e. if the Py_TPFLAGS_HAVE_GC flag bit is clear in the subtype and the tp_traverse and tp_clear fields in the subtype exist and have NULL values.

Default:

PyBaseObject_Type uses Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE.

Bit Masks:

The following bit masks are currently defined; these can be ORed together using the | operator to form the value of the tp_flags field. The macro PyType_HasFeature() takes a type and a flags value, tp and f, and checks whether tp->tp_flags & f is non-zero.

Py_TPFLAGS_HEAPTYPE¶

This bit is set when the type object itself is allocated on the heap, for example, types created dynamically using PyType_FromSpec(). In this case, the ob_type field of its instances is considered a reference to the type, and the type object is INCREF’ed when a new instance is created, and DECREF’ed when an instance is destroyed (this does not apply to instances of subtypes; only the type referenced by the instance’s ob_type gets INCREF’ed or DECREF’ed). Heap types should also support garbage collection as they can form a reference cycle with their own module object.

Inheritance:

???

Py_TPFLAGS_BASETYPE¶

Part of the Stable ABI.

This bit is set when the type can be used as the base type of another type. If this bit is clear, the type cannot be subtyped (similar to a “final” class in Java).

Inheritance:

???

Py_TPFLAGS_READY¶

This bit is set when the type object has been fully initialized by PyType_Ready().

Inheritance:

???

Py_TPFLAGS_READYING¶

This bit is set while PyType_Ready() is in the process of initializing the type object.

Inheritance:

???

Py_TPFLAGS_HAVE_GC¶

Part of the Stable ABI.

This bit is set when the object supports garbage collection. If this bit is set, memory for new instances (see tp_alloc) must be allocated using PyObject_GC_New or PyType_GenericAlloc() and deallocated (see tp_free) using PyObject_GC_Del(). More information in section Supporting Cyclic Garbage Collection.

Inheritance:

Group: Py_TPFLAGS_HAVE_GC, tp_traverse, tp_clear

The Py_TPFLAGS_HAVE_GC flag bit is inherited together with the tp_traverse and tp_clear fields, i.e. if the Py_TPFLAGS_HAVE_GC flag bit is clear in the subtype and the tp_traverse and tp_clear fields in the subtype exist and have NULL values.

Py_TPFLAGS_DEFAULT¶

Part of the Stable ABI.

This is a bitmask of all the bits that pertain to the existence of certain fields in the type object and its extension structures. Currently, it includes the following bits: Py_TPFLAGS_HAVE_STACKLESS_EXTENSION.

Inheritance:

???

Py_TPFLAGS_METHOD_DESCRIPTOR¶

Part of the Stable ABI since version 3.8.

This bit indicates that objects behave like unbound methods.

If this flag is set for type(meth), then:

• meth.__get__(obj, cls)(*args, **kwds) (with obj not None) must be equivalent to meth(obj, *args, **kwds).

• meth.__get__(None, cls)(*args, **kwds) must be equivalent to meth(*args, **kwds).

This flag enables an optimization for typical method calls like obj.meth(): it avoids creating a temporary “bound method” object for obj.meth.

Added in version 3.8.

Inheritance:

This flag is never inherited by types without the Py_TPFLAGS_IMMUTABLETYPE flag set. For extension types, it is inherited whenever tp_descr_get is inherited.

Py_TPFLAGS_MANAGED_DICT¶

This bit indicates that instances of the class have a __dict__ attribute, and that the space for the dictionary is managed by the VM.

If this flag is set, Py_TPFLAGS_HAVE_GC should also be set.

The type traverse function must call PyObject_VisitManagedDict() and its clear function must call PyObject_ClearManagedDict().

Added in version 3.12.

Inheritance:

This flag is inherited unless the tp_dictoffset field is set in a superclass.

Py_TPFLAGS_MANAGED_WEAKREF¶

This bit indicates that instances of the class should be weakly referenceable.

Added in version 3.12.

Inheritance:

This flag is inherited unless the tp_weaklistoffset field is set in a superclass.

Py_TPFLAGS_ITEMS_AT_END¶

Part of the Stable ABI since version 3.12.

Only usable with variable-size types, i.e. ones with non-zero tp_itemsize.

Indicates that the variable-sized portion of an instance of this type is at the end of the instance’s memory area, at an offset of Py_TYPE(obj)->tp_basicsize (which may be different in each subclass).

When setting this flag, be sure that all superclasses either use this memory layout, or are not variable-sized. Python does not check this.

Added in version 3.12.

Inheritance:

This flag is inherited.

Py_TPFLAGS_LONG_SUBCLASS¶

Py_TPFLAGS_LIST_SUBCLASS¶

Py_TPFLAGS_TUPLE_SUBCLASS¶

Py_TPFLAGS_BYTES_SUBCLASS¶

Py_TPFLAGS_UNICODE_SUBCLASS¶

Py_TPFLAGS_DICT_SUBCLASS¶

Py_TPFLAGS_BASE_EXC_SUBCLASS¶

Py_TPFLAGS_TYPE_SUBCLASS¶

Functions such as PyLong_Check() will call PyType_FastSubclass() with one of these flags to quickly determine if a type is a subclass of a built-in type; such specific checks are faster than a generic check, like PyObject_IsInstance(). Custom types that inherit from built-ins should have their tp_flags set appropriately, or the code that interacts with such types will behave differently depending on what kind of check is used.

Py_TPFLAGS_HAVE_FINALIZE¶

This bit is set when the tp_finalize slot is present in the type structure.

Added in version 3.4.

Deprecated since version 3.8: This flag isn’t necessary anymore, as the interpreter assumes the tp_finalize slot is always present in the type structure.

Py_TPFLAGS_HAVE_VECTORCALL¶

Part of the Stable ABI since version 3.12.

This bit is set when the class implements the vectorcall protocol. See tp_vectorcall_offset for details.

Inheritance:

This bit is inherited if tp_call is also inherited.

Added in version 3.8: as _Py_TPFLAGS_HAVE_VECTORCALL

Changed in version 3.9: Renamed to the current name, without the leading underscore. The old provisional name is soft deprecated.

Changed in version 3.12: This flag is now removed from a class when the class’s __call__() method is reassigned.

This flag can now be inherited by mutable classes.

Py_TPFLAGS_IMMUTABLETYPE¶

This bit is set for type objects that are immutable: type attributes cannot be set nor deleted.

PyType_Ready() automatically applies this flag to static types.

Inheritance:

This flag is not inherited.

Added in version 3.10.

Py_TPFLAGS_DISALLOW_INSTANTIATION¶

Disallow creating instances of the type: set tp_new to NULL and don’t create the __new__ key in the type dictionary.

The flag must be set before creating the type, not after. For example, it must be set before PyType_Ready() is called on the type.

The flag is set automatically on static types if tp_base is NULL or &PyBaseObject_Type and tp_new is NULL.

Inheritance:

This flag is not inherited. However, subclasses will not be instantiable unless they provide a non-NULL tp_new (which is only possible via the C API).

Note

To disallow instantiating a class directly but allow instantiating its subclasses (e.g. for an abstract base class), do not use this flag. Instead, make tp_new only succeed for subclasses.

Added in version 3.10.

Py_TPFLAGS_MAPPING¶

This bit indicates that instances of the class may match mapping patterns when used as the subject of a match block. It is automatically set when registering or subclassing collections.abc.Mapping, and unset when registering collections.abc.Sequence.

Note

Py_TPFLAGS_MAPPING and Py_TPFLAGS_SEQUENCE are mutually exclusive; it is an error to enable both flags simultaneously.

Inheritance:

This flag is inherited by types that do not already set Py_TPFLAGS_SEQUENCE.

See also

PEP 634 – Structural Pattern Matching: Specification

Added in version 3.10.

Py_TPFLAGS_SEQUENCE¶

This bit indicates that instances of the class may match sequence patterns when used as the subject of a match block. It is automatically set when registering or subclassing collections.abc.Sequence, and unset when registering collections.abc.Mapping.

Note

Py_TPFLAGS_MAPPING and Py_TPFLAGS_SEQUENCE are mutually exclusive; it is an error to enable both flags simultaneously.

Inheritance:

This flag is inherited by types that do not already set Py_TPFLAGS_MAPPING.

See also

PEP 634 – Structural Pattern Matching: Specification

Added in version 3.10.

Py_TPFLAGS_VALID_VERSION_TAG¶

Internal. Do not set or unset this flag. To indicate that a class has changed call PyType_Modified()

Warning

This flag is present in header files, but is not be used. It will be removed in a future version of CPython

Py_TPFLAGS_HAVE_VERSION_TAG¶

This macro does nothing. Historically, this would indicate that the tp_version_tag field was available and initialized.

Soft deprecated since version 3.13.

Py_TPFLAGS_INLINE_VALUES¶

This bit indicates that instances of this type will have an “inline values” array (containing the object’s attributes) placed directly after the end of the object.

This requires that Py_TPFLAGS_HAVE_GC is set.

Inheritance:

This flag is not inherited.

Added in version 3.13.

Py_TPFLAGS_IS_ABSTRACT¶

This bit indicates that this is an abstract type and therefore cannot be instantiated.

Inheritance:

This flag is not inherited.

See also

abc

Py_TPFLAGS_HAVE_STACKLESS_EXTENSION¶

Internal. Do not set or unset this flag. Historically, this was a reserved flag for use in Stackless Python.

Warning

This flag is present in header files, but is not be used. This may be removed in a future version of CPython.

const char *PyTypeObject.tp_doc¶

The corresponding slot ID Py_tp_doc is part of the Stable ABI.

An optional pointer to a NUL-terminated C string giving the docstring for this type object. This is exposed as the __doc__ attribute on the type and instances of the type.

Inheritance:

This field is not inherited by subtypes.

traverseproc PyTypeObject.tp_traverse¶

The corresponding slot ID Py_tp_traverse is part of the Stable ABI.

An optional pointer to a traversal function for the garbage collector. This is only used if the Py_TPFLAGS_HAVE_GC flag bit is set. The signature is:

int tp_traverse(PyObject *self, visitproc visit, void *arg);

More information about Python’s garbage collection scheme can be found in section Supporting Cyclic Garbage Collection.

The tp_traverse pointer is used by the garbage collector to detect reference cycles. A typical implementation of a tp_traverse function simply calls Py_VISIT() on each of the instance’s members that are Python objects that the instance owns. For example, this is function local_traverse() from the _thread extension module:

static int
local_traverse(PyObject *op, visitproc visit, void *arg)
{
    localobject *self = (localobject *) op;
    Py_VISIT(self->args);
    Py_VISIT(self->kw);
    Py_VISIT(self->dict);
    return 0;
}

Note that Py_VISIT() is called only on those members that can participate in reference cycles. Although there is also a self->key member, it can only be NULL or a Python string and therefore cannot be part of a reference cycle.

On the other hand, even if you know a member can never be part of a cycle, as a debugging aid you may want to visit it anyway just so the gc module’s get_referents() function will include it.

Heap types (Py_TPFLAGS_HEAPTYPE) must visit their type with:

Py_VISIT(Py_TYPE(self));

It is only needed since Python 3.9. To support Python 3.8 and older, this line must be conditional:

#if PY_VERSION_HEX >= 0x03090000
    Py_VISIT(Py_TYPE(self));
#endif

If the Py_TPFLAGS_MANAGED_DICT bit is set in the tp_flags field, the traverse function must call PyObject_VisitManagedDict() like this:

PyObject_VisitManagedDict((PyObject*)self, visit, arg);

Warning

When implementing tp_traverse, only the members that the instance owns (by having strong references to them) must be visited. For instance, if a