# Object Protocol

PyObject* `Py_NotImplemented`

  The `NotImplemented` singleton, used to signal that an operation is not implemented for the given type combination.

`Py_RETURN_NOTIMPLEMENTED`

  Properly handle returning `Py_NotImplemented` from within a C function (that is, increment the reference count of NotImplemented and return it).

int `PyObject_Print`(PyObject *o, FILE *fp, int flags)

  Print an object o, on file fp. Returns `-1` on error. The flags argument is used to enable certain printing options. The only option currently supported is `Py_PRINT_RAW`; if given, the `str()` of the object is written instead of the `repr()`.

int `PyObject_HasAttr`(PyObject *o, PyObject *attr_name)

  Returns `1` if o has the attribute attr_name, and `0` otherwise. This is equivalent to the Python expression `hasattr(o, attr_name)`. This function always succeeds.

  Note that exceptions which occur while calling `__getattr__()` and `__getattribute__()` methods will get suppressed. To get error reporting use `PyObject_GetAttr()` instead.

int `PyObject_HasAttrString`(PyObject *o, const char *attr_name)

  Returns `1` if o has the attribute attr_name, and `0` otherwise. This is equivalent to the Python expression `hasattr(o, attr_name)`. This function always succeeds.

  Note that exceptions which occur while calling `__getattr__()` and `__getattribute__()` methods and creating a temporary string object will get suppressed. To get error reporting use `PyObject_GetAttrString()` instead.

PyObject* `PyObject_GetAttr`(PyObject *o, PyObject *attr_name)
  Return value: New reference.

  Retrieve an attribute named attr_name from object o. Returns the attribute value on success, or `NULL` on failure. This is the equivalent of the Python expression `o.attr_name`.

PyObject* `PyObject_GetAttrString`(PyObject *o, const char *attr_name)
  Return value: New reference.

  Retrieve an attribute named attr_name from object o. Returns the attribute value on success, or `NULL` on failure. This is the equivalent of the Python expression `o.attr_name`.

PyObject* `PyObject_GenericGetAttr`(PyObject *o, PyObject *name)
  Return value: New reference.

  Generic attribute getter function that is meant to be put into a type object’s `tp_getattro` slot. It looks for a descriptor in the dictionary of classes in the object’s MRO as well as an attribute in the object’s `__dict__` (if present). As outlined in Implementing Descriptors, data descriptors take preference over instance attributes, while non-data descriptors don’t. Otherwise, an `AttributeError` is raised.

int `PyObject_SetAttr`(PyObject *o, PyObject *attr_name, PyObject *v)

  Set the value of the attribute named attr_name, for object o, to the value v. Raise an exception and return `-1` on failure; return `0` on success. This is the equivalent of the Python statement `o.attr_name = v`.

  If v is `NULL`, the attribute is deleted, however this feature is deprecated in favour of using `PyObject_DelAttr()`.

int `PyObject_SetAttrString`(PyObject *o, const char *attr_name, PyObject *v)

  Set the value of the attribute named attr_name, for object o, to the value v. Raise an exception and return `-1` on failure; return `0` on success. This is the equivalent of the Python statement `o.attr_name = v`.

  If v is `NULL`, the attribute is deleted, however this feature is deprecated in favour of using `PyObject_DelAttrString()`.

int `PyObject_GenericSetAttr`(PyObject *o, PyObject *name, PyObject *value)

  Generic attribute setter and deleter function that is meant to be put into a type object’s `tp_setattro` slot. It looks for a data descriptor in the dictionary of classes in the object’s MRO, and if found it takes preference over setting or deleting the attribute in the instance dictionary. Otherwise, the attribute is set or deleted in the object’s `__dict__` (if present). On success, `0` is returned, otherwise an `AttributeError` is raised and `-1` is returned.

int `PyObject_DelAttr`(PyObject *o, PyObject *attr_name)

  Delete attribute named attr_name, for object o. Returns `-1` on failure. This is the equivalent of the Python statement `del o.attr_name`.

int `PyObject_DelAttrString`(PyObject *o, const char *attr_name)

  Delete attribute named attr_name, for object o. Returns `-1` on failure. This is the equivalent of the Python statement `del o.attr_name`.

PyObject* `PyObject_GenericGetDict`(PyObject *o, void *context)
  Return value: New reference.

  A generic implementation for the getter of a `__dict__` descriptor. It creates the dictionary if necessary.

  New in version 3.3.

int `PyObject_GenericSetDict`(PyObject *o, PyObject *value, void *context)

  A generic implementation for the setter of a `__dict__` descriptor. This implementation does not allow the dictionary to be deleted.

  New in version 3.3.

PyObject* `PyObject_RichCompare`(PyObject *o1, PyObject *o2, int opid)
  Return value: New reference.

  Compare the values of o1 and o2 using the operation specified by opid, which must be one of `Py_LT`, `Py_LE`, `Py_EQ`, `Py_NE`, `Py_GT`, or `Py_GE`, corresponding to `<`, `<=`, `==`, `!=`, `>`, or `>=` respectively. This is the equivalent of the Python expression `o1 op o2`, where `op` is the operator corresponding to opid. Returns the value of the comparison on success, or `NULL` on failure.

int `PyObject_RichCompareBool`(PyObject *o1, PyObject *o2, int opid)

  Compare the values of o1 and o2 using the operation specified by opid, which must be one of `Py_LT`, `Py_LE`, `Py_EQ`, `Py_NE`, `Py_GT`, or `Py_GE`, corresponding to `<`, `<=`, `==`, `!=`, `>`, or `>=` respectively. Returns `-1` on error, `0` if the result is false, `1` otherwise. This is the equivalent of the Python expression `o1 op o2`, where `op` is the operator corresponding to opid.

Note

If o1 and o2 are the same object, `PyObject_RichCompareBool()` will always return `1` for `Py_EQ` and `0` for `Py_NE`.

PyObject* `PyObject_Repr`(PyObject *o)
  Return value: New reference.

  Compute a string representation of object o. Returns the string representation on success, `NULL` on failure. This is the equivalent of the Python expression `repr(o)`. Called by the `repr()` built-in function.

  Changed in version 3.4: This function now includes a debug assertion to help ensure that it does not silently discard an active exception.

PyObject* `PyObject_ASCII`(PyObject *o)
  Return value: New reference.

  As `PyObject_Repr()`, compute a string representation of object o, but escape the non-ASCII characters in the string returned by `PyObject_Repr()` with `\x`, `\u` or `\U` escapes. This generates a string similar to that returned by `PyObject_Repr()` in Python 2. Called by the `ascii()` built-in function.

PyObject* `PyObject_Str`(PyObject *o)
  Return value: New reference.

  Compute a string representation of object o. Returns the string representation on success, `NULL` on failure. This is the equivalent of the Python expression `str(o)`. Called by the `str()` built-in function and, therefore, by the `print()` function.

  Changed in version 3.4: This function now includes a debug assertion to help ensure that it does not silently discard an active exception.

PyObject* `PyObject_Bytes`(PyObject *o)
  Return value: New reference.

  Compute a bytes representation of object o. `NULL` is returned on failure and a bytes object on success. This is equivalent to the Python expression `bytes(o)`, when o is not an integer. Unlike `bytes(o)`, a TypeError is raised when o is an integer instead of a zero-initialized bytes object.

int `PyObject_IsSubclass`(PyObject *derived, PyObject *cls)

  Return `1` if the class derived is identical to or derived from the class cls, otherwise return `0`. In case of an error, return `-1`.

  If cls is a tuple, the check will be done against every entry in cls. The result will be `1` when at least one of the checks returns `1`, otherwise it will be `0`.

  If cls has a `__subclasscheck__()` method, it will be called to determine the subclass status as described in PEP 3119. Otherwise, derived is a subclass of cls if it is a direct or indirect subclass, i.e. contained in `cls.__mro__`.

  Normally only class objects, i.e. instances of `type` or a derived class, are considered classes. However, objects can override this by having a `__bases__` attribute (which must be a tuple of base classes).

int `PyObject_IsInstance`(PyObject *inst, PyObject *cls)

  Return `1` if inst is an instance of the class cls or a subclass of cls, or `0` if not. On error, returns `-1` and sets an exception.

  If cls is a tuple, the check will be done against every entry in cls. The result will be `1` when at least one of the checks returns `1`, otherwise it will be `0`.

  If cls has a `__instancecheck__()` method, it will be called to determine the subclass status as described in PEP 3119. Otherwise, inst is an instance of cls if its class is a subclass of cls.

  An instance inst can override what is considered its class by having a `__class__` attribute.

  An object cls can override if it is considered a class, and what its base classes are, by having a `__bases__` attribute (which must be a tuple of base classes).

int `PyCallable_Check`(PyObject *o)

  Determine if the object o is callable. Return `1` if the object is callable and `0` otherwise. This function always succeeds.

PyObject* `PyObject_Call`(PyObject *callable, PyObject *args, PyObject *kwargs)
  Return value: New reference.

  Call a callable Python object callable, with arguments given by the tuple args, and named arguments given by the dictionary kwargs.

  args must not be `NULL`, use an empty tuple if no arguments are needed. If no named arguments are needed, kwargs can be `NULL`.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This is the equivalent of the Python expression: `callable(*args, **kwargs)`.

PyObject* `PyObject_CallObject`(PyObject *callable, PyObject *args)
  Return value: New reference.

  Call a callable Python object callable, with arguments given by the tuple args. If no arguments are needed, then args can be `NULL`.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This is the equivalent of the Python expression: `callable(*args)`.

PyObject* `PyObject_CallFunction`(PyObject *callable, const char *format, ...)
  Return value: New reference.

  Call a callable Python object callable, with a variable number of C arguments. The C arguments are described using a `Py_BuildValue()` style format string. The format can be `NULL`, indicating that no arguments are provided.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This is the equivalent of the Python expression: `callable(*args)`.

  Note that if you only pass `PyObject *` args, `PyObject_CallFunctionObjArgs()` is a faster alternative.

  Changed in version 3.4: The type of format was changed from `char *`.

PyObject* `PyObject_CallMethod`(PyObject *obj, const char *name, const char *format, ...)
  Return value: New reference.

  Call the method named name of object obj with a variable number of C arguments. The C arguments are described by a `Py_BuildValue()` format string that should produce a tuple.

  The format can be `NULL`, indicating that no arguments are provided.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This is the equivalent of the Python expression: `obj.name(arg1, arg2, ...)`.

  Note that if you only pass `PyObject *` args, `PyObject_CallMethodObjArgs()` is a faster alternative.

  Changed in version 3.4: The types of name and format were changed from `char *`.

PyObject* `PyObject_CallFunctionObjArgs`(PyObject *callable, ..., NULL)
  Return value: New reference.

  Call a callable Python object callable, with a variable number of `PyObject*` arguments. The arguments are provided as a variable number of parameters followed by `NULL`.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This is the equivalent of the Python expression: `callable(arg1, arg2, ...)`.

PyObject* `PyObject_CallMethodObjArgs`(PyObject *obj, PyObject *name, ..., NULL)
  Return value: New reference.

  Calls a method of the Python object obj, where the name of the method is given as a Python string object in name. It is called with a variable number of `PyObject*` arguments. The arguments are provided as a variable number of parameters followed by `NULL`.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

PyObject* `_PyObject_Vectorcall`(PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwnames)

  Call a callable Python object callable, using `vectorcall` if possible.

  args is a C array with the positional arguments.

  nargsf is the number of positional arguments plus optionally the flag `PY_VECTORCALL_ARGUMENTS_OFFSET` (see below). To get actual number of arguments, use `PyVectorcall_NARGS(nargsf)`.

  kwnames can be either `NULL` (no keyword arguments) or a tuple of keyword names. In the latter case, the values of the keyword arguments are stored in args after the positional arguments. The number of keyword arguments does not influence nargsf.

  kwnames must contain only objects of type `str` (not a subclass), and all keys must be unique.

  Return the result of the call on success, or raise an exception and return `NULL` on failure.

  This uses the vectorcall protocol if the callable supports it; otherwise, the arguments are converted to use `tp_call`.

  Note

  This function is provisional and expected to become public in Python 3.9, with a different name and, possibly, changed semantics. If you use the function, plan for updating your code for Python 3.9.

  New in version 3.8.

`PY_VECTORCALL_ARGUMENTS_OFFSET`

  If set in a vectorcall nargsf argument, the callee is allowed to temporarily change `args[-1]`. In other words, args points to argument 1 (not 0) in the allocated vector. The callee must restore the value of `args[-1]` before returning.

  Whenever they can do so cheaply (without additional allocation), callers are encouraged to use `PY_VECTORCALL_ARGUMENTS_OFFSET`. Doing so will allow callables such as bound methods to make their onward calls (which include a prepended self argument) cheaply.

  New in version 3.8.

Py_ssize_t `PyVectorcall_NARGS`(size_t nargsf)

  Given a vectorcall nargsf argument, return the actual number of arguments. Currently equivalent to `nargsf & ~PY_VECTORCALL_ARGUMENTS_OFFSET`.

  New in version 3.8.

PyObject* `_PyObject_FastCallDict`(PyObject *callable, PyObject *const *args, size_t nargsf, PyObject *kwdict)

  Same as `_PyObject_Vectorcall()` except that the keyword arguments are passed as a dictionary in kwdict. This may be `NULL` if there are no keyword arguments.

  For callables supporting `vectorcall`, the arguments are internally converted to the vectorcall convention. Therefore, this function adds some overhead compared to `_PyObject_Vectorcall()`. It should only be used if the caller already has a dictionary ready to use.

  Note

  This function is provisional and expected to become public in Python 3.9, with a different name and, possibly, changed semantics. If you use the function, plan for updating your code for Python 3.9.

  New in version 3.8.

Py_hash_t `PyObject_Hash`(PyObject *o)

  Compute and return the hash value of an object o. On failure, return `-1`. This is the equivalent of the Python expression `hash(o)`.

  Changed in version 3.2: The return type is now Py_hash_t. This is a signed integer the same size as Py_ssize_t.

Py_hash_t `PyObject_HashNotImplemented`(PyObject *o)

  Set a `TypeError` indicating that `type(o)` is not hashable and return `-1`. This function receives special treatment when stored in a `tp_hash` slot, allowing a type to explicitly indicate to the interpreter that it is not hashable.

int `PyObject_IsTrue`(PyObject *o)

  Returns `1` if the object o is considered to be true, and `0` otherwise. This is equivalent to the Python expression `not not o`. On failure, return `-1`.

int `PyObject_Not`(PyObject *o)

  Returns `0` if the object o is considered to be true, and `1` otherwise. This is equivalent to the Python expression `not o`. On failure, return `-1`.

PyObject* `PyObject_Type`(PyObject *o)
  Return value: New reference.

  When o is non-`NULL`, returns a type object corresponding to the object type of object o. On failure, raises `SystemError` and returns `NULL`. This is equivalent to the Python expression `type(o)`. This function increments the reference count of the return value. There’s really no reason to use this function instead of the common expression `o->ob_type`, which returns a pointer of type `PyTypeObject*`, except when the incremented reference count is needed.

int `PyObject_TypeCheck`(PyObject *o, PyTypeObject *type)

  Return true if the object o is of type type or a subtype of type. Both parameters must be non-`NULL`.

Py_ssize_t `PyObject_Size`(PyObject *o)
Py_ssize_t `PyObject_Length`(PyObject *o)

  Return the length of object o. If the object o provides either the sequence and mapping protocols, the sequence length is returned. On error, `-1` is returned. This is the equivalent to the Python expression `len(o)`.

Py_ssize_t `PyObject_LengthHint`(PyObject *o, Py_ssize_t default)

  Return an estimated length for the object o. First try to return its actual length, then an estimate using `__length_hint__()`, and finally return the default value. On error return `-1`. This is the equivalent to the Python expression `operator.length_hint(o, default)`.

  New in version 3.4.

PyObject* `PyObject_GetItem`(PyObject *o, PyObject *key)
  Return value: New reference.

  Return element of o corresponding to the object key or `NULL` on failure. This is the equivalent of the Python expression `o[key]`.

int `PyObject_SetItem`(PyObject *o, PyObject *key, PyObject *v)

  Map the object key to the value v. Raise an exception and return `-1` on failure; return `0` on success. This is the equivalent of the Python statement `o[key] = v`. This function does not steal a reference to v.

int `PyObject_DelItem`(PyObject *o, PyObject *key)

  Remove the mapping for the object key from the object o. Return `-1` on failure. This is equivalent to the Python statement `del o[key]`.

PyObject* `PyObject_Dir`(PyObject *o)
  Return value: New reference.

  This is equivalent to the Python expression `dir(o)`, returning a (possibly empty) list of strings appropriate for the object argument, or `NULL` if there was an error. If the argument is `NULL`, this is like the Python `dir()`, returning the names of the current locals; in this case, if no execution frame is active then `NULL` is returned but `PyErr_Occurred()` will return false.

PyObject* `PyObject_GetIter`(PyObject *o)
  Return value: New reference.

  This is equivalent to the Python expression `iter(o)`. It returns a new iterator for the object argument, or the object itself if the object is already an iterator. Raises `TypeError` and returns `NULL` if the object cannot be iterated.