Type Objects¶

Perhaps one of the most important structures of the Python object system is the structure that defines a new type: the PyTypeObject structure. Type objects can be handled using any of the PyObject_*() or PyType_*() functions, but do not offer much that’s interesting to most Python applications. These objects are fundamental to how objects behave, so they are very important to the interpreter itself and to any extension module that implements new types.

Type objects are fairly large compared to most of the standard types. The reason for the size is that each type object stores a large number of values, mostly C function pointers, each of which implements a small part of the type’s functionality. The fields of the type object are examined in detail in this section. The fields will be described in the order in which they occur in the structure.

Typedefs: unaryfunc, binaryfunc, ternaryfunc, inquiry, coercion, intargfunc, intintargfunc, intobjargproc, intintobjargproc, objobjargproc, destructor, freefunc, printfunc, getattrfunc, getattrofunc, setattrfunc, setattrofunc, cmpfunc, reprfunc, hashfunc

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

typedef struct _typeobject {
    PyObject_VAR_HEAD
    char *tp_name; /* For printing, in format "<module>.<name>" */
    int 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;

    /* 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 */
    long tp_flags;

    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 */
    long tp_weaklistoffset;

    /* Added in release 2.2 */
    /* Iterators */
    getiterfunc tp_iter;
    iternextfunc tp_iternext;

    /* Attribute descriptor and subclassing stuff */
    struct PyMethodDef *tp_methods;
    struct PyMemberDef *tp_members;
    struct PyGetSetDef *tp_getset;
    struct _typeobject *tp_base;
    PyObject *tp_dict;
    descrgetfunc tp_descr_get;
    descrsetfunc tp_descr_set;
    long 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;
    PyObject *tp_subclasses;
    PyObject *tp_weaklist;

} PyTypeObject;

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* PyObject._ob_next¶

PyObject* PyObject._ob_prev¶

These fields are only present when the macro Py_TRACE_REFS is defined. Their initialization to NULL is taken care of by the PyObject_HEAD_INIT macro. For statically allocated objects, these fields always remain NULL. For dynamically allocated objects, these two fields are used to link the object into a doubly-linked list of all live objects on the heap. This could be used for various debugging purposes; currently the only use is to print the objects that are still alive at the end of a run when the environment variable PYTHONDUMPREFS is set.

These fields are not inherited by subtypes.

Py_ssize_t PyObject.ob_refcnt¶

This is the type object’s reference count, 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.

This field is not inherited by subtypes.

Changed in version 2.5: This field used to be an int type. This might require changes in your code for properly supporting 64-bit systems.

PyTypeObject* 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: in Python 2.2, it is set to &PyType_Type; in Python 2.2.1 and later it is initialized to the ob_type field of the base class. PyType_Ready() will not change this field if it is non-zero.

In Python 2.2, this field is not inherited by subtypes. In 2.2.1, and in 2.3 and beyond, it is inherited by subtypes.

Py_ssize_t 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 is not inherited by subtypes.

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 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.

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. The value of N is typically stored in the instance’s ob_size field. There are exceptions: for example, long ints use a negative ob_size to indicate a negative number, and N is abs(ob_size) there. 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 structure for the list type has fixed-length instances, yet those instances have a meaningful ob_size field).

The basic size includes the fields in the instance declared by the macro PyObject_HEAD or PyObject_VAR_HEAD (whichever is used to declare the instance struct) and this in turn includes the _ob_prev and _ob_next fields if they are present. This means that the only correct way to get an initializer for the tp_basicsize is to use the sizeof operator on the struct used to declare the instance layout. The basic size does not include the GC header size (this is new in Python 2.2; in 2.1 and 2.0, the GC header size was included in tp_basicsize).

These fields are inherited separately by subtypes. 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).

A note about alignment: if the variable items require a particular alignment, this should be taken care of by the value of tp_basicsize. Example: suppose a type implements an array of double. tp_itemsize is sizeof(double). It is the programmer’s responsibility that tp_basicsize is a multiple of sizeof(double) (assuming this is the alignment requirement for double).

destructor PyTypeObject.tp_dealloc¶

A pointer to the instance destructor function. This function must be defined unless the type guarantees that its instances will never be deallocated (as is the case for the singletons None and Ellipsis).

The destructor function is called by the Py_DECREF() and Py_XDECREF() macros when the new reference count is zero. At this point, the instance is still in existence, but there are no references to it. The destructor function should free all references which the instance owns, free all memory buffers owned by the instance (using the freeing function corresponding to the allocation function used to allocate the buffer), and finally (as its last action) call the type’s tp_free function. If the type is not subtypable (doesn’t have the Py_TPFLAGS_BASETYPE flag bit set), it is permissible to call the object deallocator directly instead of via tp_free. The object deallocator should be the one used to allocate the instance; this is normally PyObject_Del() if the instance was allocated using PyObject_New() or PyObject_VarNew(), or PyObject_GC_Del() if the instance was allocated using PyObject_GC_New() or PyObject_GC_NewVar().

This field is inherited by subtypes.

printfunc PyTypeObject.tp_print¶

An optional pointer to the instance print function.

The print function is only called when the instance is printed to a real file; when it is printed to a pseudo-file (like a StringIO instance), the instance’s tp_repr or tp_str function is called to convert it to a string. These are also called when the type’s tp_print field is NULL. A type should never implement tp_print in a way that produces different output than tp_repr or tp_str would.

The print function is called with the same signature as PyObject_Print(): int tp_print(PyObject *self, FILE *file, int flags). The self argument is the instance to be printed. The file argument is the stdio file to which it is to be printed. The flags argument is composed of flag bits. The only flag bit currently defined is Py_PRINT_RAW. When the Py_PRINT_RAW flag bit is set, the instance should be printed the same way as tp_str would format it; when the Py_PRINT_RAW flag bit is clear, the instance should be printed the same was as tp_repr would format it. It should return -1 and set an exception condition when an error occurred during the comparison.

It is possible that the tp_print field will be deprecated. In any case, it is recommended not to define tp_print, but instead to rely on tp_repr and tp_str for printing.

This field is inherited by subtypes.

getattrfunc PyTypeObject.tp_getattr¶

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. The signature is

PyObject * tp_getattr(PyObject *o, char *attr_name);

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¶

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. The signature is

PyObject * tp_setattr(PyObject *o, char *attr_name, PyObject *v);

The v argument is set to NULL to delete the attribute. 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.

cmpfunc PyTypeObject.tp_compare¶

An optional pointer to the three-way comparison function.

The signature is the same as for PyObject_Compare(). The function should return 1 if self greater than other, 0 if self is equal to other, and -1 if self less than other. It should return -1 and set an exception condition when an error occurred during the comparison.

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

reprfunc PyTypeObject.tp_repr¶

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

The signature is the same as for PyObject_Repr(); it 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.

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.

This field is inherited by subtypes.

PyNumberMethods* 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.

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

PySequenceMethods* 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.

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

PyMappingMethods* 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.

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

hashfunc PyTypeObject.tp_hash¶

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

The signature is the same as for PyObject_Hash(); it must return a C long. 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.

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().

When this field is not set, two possibilities exist: if the tp_compare and tp_richcompare fields are both NULL, a default hash value based on the object’s address is returned; otherwise, a TypeError is raised.

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

ternaryfunc PyTypeObject.tp_call¶

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().

This field is inherited by subtypes.

reprfunc PyTypeObject.tp_str¶

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(); it must return a string or a Unicode object. This function should return a “friendly” string representation of the object, as this is the representation that will be used by the print statement.

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

This field is inherited by subtypes.

getattrofunc PyTypeObject.tp_getattro¶

An optional pointer to the get-attribute function.

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

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.

setattrofunc PyTypeObject.tp_setattro¶

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

The signature is the same as for PyObject_SetAttr(), but setting v 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.

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.

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.

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

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 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 (as indicated by the Py_TPFLAGS_HAVE_RICHCOMPARE flag bit) and have NULL values.

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_HAVE_GETCHARBUFFER¶: If this bit is set, the PyBufferProcs struct referenced by tp_as_buffer has the bf_getcharbuffer field.

Py_TPFLAGS_HAVE_SEQUENCE_IN¶: If this bit is set, the PySequenceMethods struct referenced by tp_as_sequence has the sq_contains field.

Py_TPFLAGS_GC¶: This bit is obsolete. The bit it used to name is no longer in use. The symbol is now defined as zero.

Py_TPFLAGS_HAVE_INPLACEOPS¶: If this bit is set, the PySequenceMethods struct referenced by tp_as_sequence and the PyNumberMethods structure referenced by tp_as_number contain the fields for in-place operators. In particular, this means that the PyNumberMethods structure has the fields nb_inplace_add, nb_inplace_subtract, nb_inplace_multiply, nb_inplace_divide, nb_inplace_remainder, nb_inplace_power, nb_inplace_lshift, nb_inplace_rshift, nb_inplace_and, nb_inplace_xor, and nb_inplace_or; and the PySequenceMethods struct has the fields sq_inplace_concat and sq_inplace_repeat.

Py_TPFLAGS_CHECKTYPES¶: If this bit is set, the binary and ternary operations in the PyNumberMethods structure referenced by tp_as_number accept arguments of arbitrary object types, and do their own type conversions if needed. If this bit is clear, those operations require that all arguments have the current type as their type, and the caller is supposed to perform a coercion operation first. This applies to nb_add, nb_subtract, nb_multiply, nb_divide, nb_remainder, nb_divmod, nb_power, nb_lshift, nb_rshift, nb_and, nb_xor, and nb_or.

Py_TPFLAGS_HAVE_RICHCOMPARE¶: If this bit is set, the type object has the tp_richcompare field, as well as the tp_traverse and the tp_clear fields.

Py_TPFLAGS_HAVE_WEAKREFS¶: If this bit is set, the tp_weaklistoffset field is defined. Instances of a type are weakly referenceable if the type’s tp_weaklistoffset field has a value greater than zero.

Py_TPFLAGS_HAVE_ITER¶: If this bit is set, the type object has the tp_iter and tp_iternext fields.

Py_TPFLAGS_HAVE_CLASS¶: If this bit is set, the type object has several new fields defined starting in Python 2.2: tp_methods, tp_members, tp_getset, tp_base, tp_dict, tp_descr_get, tp_descr_set, tp_dictoffset, tp_init, tp_alloc, tp_new, tp_free, tp_is_gc, tp_bases, tp_mro, tp_cache, tp_subclasses, and tp_weaklist.

Py_TPFLAGS_HEAPTYPE¶: This bit is set when the type object itself is allocated on the heap. 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).

Py_TPFLAGS_BASETYPE¶: 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).

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

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

Py_TPFLAGS_HAVE_GC¶: This bit is set when the object supports garbage collection. If this bit is set, instances must be created using PyObject_GC_New() and destroyed using PyObject_GC_Del(). More information in section Supporting Cyclic Garbage Collection. This bit also implies that the GC-related fields tp_traverse and tp_clear are present in the type object; but those fields also exist when Py_TPFLAGS_HAVE_GC is clear but Py_TPFLAGS_HAVE_RICHCOMPARE is set.

Py_TPFLAGS_DEFAULT¶: 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_GETCHARBUFFER, Py_TPFLAGS_HAVE_SEQUENCE_IN, Py_TPFLAGS_HAVE_INPLACEOPS, Py_TPFLAGS_HAVE_RICHCOMPARE, Py_TPFLAGS_HAVE_WEAKREFS, Py_TPFLAGS_HAVE_ITER, and Py_TPFLAGS_HAVE_CLASS.

char* PyTypeObject.tp_doc¶

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.

This field is not inherited by subtypes.

The following three fields only exist if the Py_TPFLAGS_HAVE_RICHCOMPARE flag bit is set.

traverseproc PyTypeObject.tp_traverse¶

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. 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. For example, this is function local_traverse() from the thread extension module:

static int
local_traverse(localobject *self, visitproc visit, void *arg)
{
    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.

Note that Py_VISIT() requires the visit and arg parameters to local_traverse() to have these specific names; don’t name them just anything.

This field is inherited by subtypes together with tp_clear and the Py_TPFLAGS_HAVE_GC flag bit: the flag bit, tp_traverse, and tp_clear are all inherited from the base type if they are all zero in the subtype and the subtype has the Py_TPFLAGS_HAVE_RICHCOMPARE flag bit set.

inquiry PyTypeObject.tp_clear¶

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

The tp_clear member function is used to break reference cycles in cyclic garbage detected by the garbage collector. Taken together, all tp_clear functions in the system must combine to break all reference cycles. This is subtle, and if in any doubt supply a tp_clear function. For example, the tuple type does not implement a tp_clear function, because it’s possible to prove that no reference cycle can be composed entirely of tuples. Therefore the tp_clear functions of other types must be sufficient to break any cycle containing a tuple. This isn’t immediately obvious, and there’s rarely a good reason to avoid implementing tp_clear.

Implementations of tp_clear should drop the instance’s references to those of its members that may be Python objects, and set its pointers to those members to NULL, as in the following example:

static int
local_clear(localobject *self)
{
    Py_CLEAR(self->key);
    Py_CLEAR(self->args);
    Py_CLEAR(self->kw);
    Py_CLEAR(self->dict);
    return 0;
}

The Py_CLEAR() macro should be used, because clearing references is delicate: the reference to the contained object must not be decremented until after the pointer to the contained object is set to NULL. This is because decrementing the reference count may cause the contained object to become trash, triggering a chain of reclamation activity that may include invoking arbitrary Python code (due to finalizers, or weakref callbacks, associated with the contained object). If it’s possible for such code to reference self again, it’s important that the pointer to the contained object be NULL at that time, so that self knows the contained object can no longer be used. The Py_CLEAR() macro performs the operations in a safe order.

Because the goal of tp_clear functions is to break reference cycles, it’s not necessary to clear contained objects like Python strings or Python integers, which can’t participate in reference cycles. On the other hand, it may be convenient to clear all contained Python objects, and write the type’s tp_dealloc function to invoke tp_clear.

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

This field is inherited by subtypes together with tp_traverse and the Py_TPFLAGS_HAVE_GC flag bit: the flag bit, tp_traverse, and tp_clear are all inherited from the base type if they are all zero in the subtype and the subtype has the Py_TPFLAGS_HAVE_RICHCOMPARE flag bit set.

richcmpfunc PyTypeObject.tp_richcompare¶

An optional pointer to the rich comparison function, whose signature is PyObject *tp_richcompare(PyObject *a, PyObject *b, int op).

The function should return the result of the comparison (usually Py_True or Py_False). If the comparison is undefined, it must return Py_NotImplemented, if another error occurred it must return NULL and set an exception condition.

Note

If you want to implement a type for which only a limited set of comparisons makes sense (e.g. == and !=, but not < and friends), directly raise