.. highlightlang:: c

.. _object:

Object Protocol

===============

.. cfunction:: 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 :const:`Py_PRINT_RAW`; if given, the :func:`str` of the object is written

   instead of the :func:`repr`.

.. cfunction:: 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.

.. cfunction:: 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.

.. cfunction:: PyObject* PyObject_GetAttr(PyObject *o, PyObject *attr_name)

   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``.

.. cfunction:: PyObject* PyObject_GetAttrString(PyObject *o, const char *attr_name)

   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``.

.. cfunction:: 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*. Returns ``-1`` on failure.  This is the equivalent of the Python statement

   ``o.attr_name = v``.

.. cfunction:: 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*. Returns ``-1`` on failure.  This is the equivalent of the Python statement

   ``o.attr_name = v``.

.. cfunction:: 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``.

.. cfunction:: 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``.

.. cfunction:: PyObject* PyObject_RichCompare(PyObject *o1, PyObject *o2, int opid)

   Compare the values of *o1* and *o2* using the operation specified by *opid*,

   which must be one of :const:`Py_LT`, :const:`Py_LE`, :const:`Py_EQ`,

   :const:`Py_NE`, :const:`Py_GT`, or :const:`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.

.. cfunction:: 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 :const:`Py_LT`, :const:`Py_LE`, :const:`Py_EQ`,

   :const:`Py_NE`, :const:`Py_GT`, or :const:`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*.

.. cfunction:: int PyObject_Cmp(PyObject *o1, PyObject *o2, int *result)

   .. index:: builtin: cmp

   Compare the values of *o1* and *o2* using a routine provided by *o1*, if one

   exists, otherwise with a routine provided by *o2*.  The result of the comparison

   is returned in *result*.  Returns ``-1`` on failure.  This is the equivalent of

   the Python statement ``result = cmp(o1, o2)``.

.. cfunction:: int PyObject_Compare(PyObject *o1, PyObject *o2)

   .. index:: builtin: cmp

   Compare the values of *o1* and *o2* using a routine provided by *o1*, if one

   exists, otherwise with a routine provided by *o2*.  Returns the result of the

   comparison on success.  On error, the value returned is undefined; use

   :cfunc:`PyErr_Occurred` to detect an error.  This is equivalent to the Python

   expression ``cmp(o1, o2)``.

.. cfunction:: PyObject* PyObject_Repr(PyObject *o)

   .. index:: builtin: repr

   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 :func:`repr` built-in function and

   by reverse quotes.

.. cfunction:: PyObject* PyObject_Str(PyObject *o)

   .. index:: builtin: str

   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 :func:`str` built-in function and

   by the :keyword:`print` statement.

.. cfunction:: PyObject* PyObject_Bytes(PyObject *o)

   .. index:: builtin: bytes

   Compute a bytes representation of object *o*.  In 2.x, this is just a alias

   for :cfunc:`PyObject_Str`.

.. cfunction:: PyObject* PyObject_Unicode(PyObject *o)

   .. index:: builtin: unicode

   Compute a Unicode string representation of object *o*.  Returns the Unicode

   string representation on success, *NULL* on failure. This is the equivalent of

   the Python expression ``unicode(o)``.  Called by the :func:`unicode` built-in

   function.

.. cfunction:: int PyObject_IsInstance(PyObject *inst, PyObject *cls)

   Returns ``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 type object rather than a class object, :cfunc:`PyObject_IsInstance`

   returns ``1`` if *inst* is of type *cls*.  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 *inst* is not a

   class instance and *cls* is neither a type object, nor a class object, nor a

   tuple, *inst* must have a :attr:`__class__` attribute --- the class relationship

   of the value of that attribute with *cls* will be used to determine the result

   of this function.

   .. versionadded:: 2.1

   .. versionchanged:: 2.2

      Support for a tuple as the second argument added.

Subclass determination is done in a fairly straightforward way, but includes a

wrinkle that implementors of extensions to the class system may want to be aware

of.  If :class:`A` and :class:`B` are class objects, :class:`B` is a subclass of

:class:`A` if it inherits from :class:`A` either directly or indirectly.  If

either is not a class object, a more general mechanism is used to determine the

class relationship of the two objects.  When testing if *B* is a subclass of

*A*, if *A* is *B*, :cfunc:`PyObject_IsSubclass` returns true.  If *A* and *B*

are different objects, *B*'s :attr:`__bases__` attribute is searched in a

depth-first fashion for *A* --- the presence of the :attr:`__bases__` attribute

is considered sufficient for this determination.

.. cfunction:: int PyObject_IsSubclass(PyObject *derived, PyObject *cls)

   Returns ``1`` if the class *derived* is identical to or derived from the class

   *cls*, otherwise returns ``0``.  In case of an error, returns ``-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 either *derived* or *cls* is not an actual class object (or tuple),

   this function uses the generic algorithm described above.

   .. versionadded:: 2.1

   .. versionchanged:: 2.3

      Older versions of Python did not support a tuple as the second argument.

.. cfunction:: 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.

.. cfunction:: PyObject* PyObject_Call(PyObject *callable_object, PyObject *args, PyObject *kw)

   .. index:: builtin: apply

   Call a callable Python object *callable_object*, with arguments given by the

   tuple *args*, and named arguments given by the dictionary *kw*. If no named

   arguments are needed, *kw* may be *NULL*. *args* must not be *NULL*, use an

   empty tuple if no arguments are needed. Returns the result of the call on

   success, or *NULL* on failure.  This is the equivalent of the Python expression

   ``apply(callable_object, args, kw)`` or ``callable_object(*args, **kw)``.

   .. versionadded:: 2.2

.. cfunction:: PyObject* PyObject_CallObject(PyObject *callable_object, PyObject *args)

   .. index:: builtin: apply

   Call a callable Python object *callable_object*, with arguments given by the

   tuple *args*.  If no arguments are needed, then *args* may be *NULL*.  Returns

   the result of the call on success, or *NULL* on failure.  This is the equivalent

   of the Python expression ``apply(callable_object, args)`` or

   ``callable_object(*args)``.

.. cfunction:: PyObject* PyObject_CallFunction(PyObject *callable, char *format, ...)

   .. index:: builtin: apply

   Call a callable Python object *callable*, with a variable number of C arguments.

   The C arguments are described using a :cfunc:`Py_BuildValue` style format

   string.  The format may be *NULL*, indicating that no arguments are provided.

   Returns the result of the call on success, or *NULL* on failure.  This is the

   equivalent of the Python expression ``apply(callable, args)`` or

   ``callable(*args)``. Note that if you only pass :ctype:`PyObject \*` args,

   :cfunc:`PyObject_CallFunctionObjArgs` is a faster alternative.

.. cfunction:: PyObject* PyObject_CallMethod(PyObject *o, char *method, char *format, ...)

   Call the method named *method* of object *o* with a variable number of C

   arguments.  The C arguments are described by a :cfunc:`Py_BuildValue` format

   string that should  produce a tuple.  The format may be *NULL*, indicating that

   no arguments are provided. Returns the result of the call on success, or *NULL*

   on failure.  This is the equivalent of the Python expression ``o.method(args)``.

   Note that if you only pass :ctype:`PyObject \*` args,

   :cfunc:`PyObject_CallMethodObjArgs` is a faster alternative.

.. cfunction:: PyObject* PyObject_CallFunctionObjArgs(PyObject *callable, ..., NULL)

   Call a callable Python object *callable*, with a variable number of

   :ctype:`PyObject\*` arguments.  The arguments are provided as a variable number

   of parameters followed by *NULL*. Returns the result of the call on success, or

   *NULL* on failure.

   .. versionadded:: 2.2

.. cfunction:: PyObject* PyObject_CallMethodObjArgs(PyObject *o, PyObject *name, ..., NULL)

   Calls a method of the object *o*, where the name of the method is given as a

   Python string object in *name*.  It is called with a variable number of

   :ctype:`PyObject\*` arguments.  The arguments are provided as a variable number

   of parameters followed by *NULL*. Returns the result of the call on success, or

   *NULL* on failure.

   .. versionadded:: 2.2

.. cfunction:: long PyObject_Hash(PyObject *o)

   .. index:: builtin: hash

   Compute and return the hash value of an object *o*.  On failure, return ``-1``.

   This is the equivalent of the Python expression ``hash(o)``.

.. cfunction:: long PyObject_HashNotImplemented(PyObject *o)

   Set a :exc:`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.

   .. versionadded:: 2.6

.. cfunction:: 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``.

.. cfunction:: 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``.

.. cfunction:: PyObject* PyObject_Type(PyObject *o)

   .. index:: builtin: type

   When *o* is non-*NULL*, returns a type object corresponding to the object type

   of object *o*. On failure, raises :exc:`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 :ctype:`PyTypeObject\*`, except when the incremented reference

   count is needed.

.. cfunction:: 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*.

   .. versionadded:: 2.2

.. cfunction:: Py_ssize_t PyObject_Length(PyObject *o)

               Py_ssize_t PyObject_Size(PyObject *o)

   .. index:: builtin: len

   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)``.

.. cfunction:: PyObject* PyObject_GetItem(PyObject *o, PyObject *key)

   Return element of *o* corresponding to the object *key* or *NULL* on failure.

   This is the equivalent of the Python expression ``o[key]``.

.. cfunction:: int PyObject_SetItem(PyObject *o, PyObject *key, PyObject *v)

   Map the object *key* to the value *v*.  Returns ``-1`` on failure.  This is the

   equivalent of the Python statement ``o[key] = v``.

.. cfunction:: int PyObject_DelItem(PyObject *o, PyObject *key)

   Delete the mapping for *key* from *o*.  Returns ``-1`` on failure. This is the

   equivalent of the Python statement ``del o[key]``.

.. cfunction:: int PyObject_AsFileDescriptor(PyObject *o)

   Derives a file descriptor from a Python object.  If the object is an integer or

   long integer, its value is returned.  If not, the object's :meth:`fileno` method

   is called if it exists; the method must return an integer or long integer, which

   is returned as the file descriptor value.  Returns ``-1`` on failure.

.. cfunction:: PyObject* PyObject_Dir(PyObject *o)

   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 :cfunc:`PyErr_Occurred` will return false.

.. cfunction:: PyObject* PyObject_GetIter(PyObject *o)

   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 :exc:`TypeError` and returns *NULL* if the object cannot be

   iterated.