cpython/Doc/c-api/object.rst

.. 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, therefore, by the :func:`print` function.


.. 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.


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.


.. 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)

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


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

   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 ``callable_object(*args)``.


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

   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 ``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.


.. 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.


.. 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:: 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*.


.. 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:: 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.