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.. 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:: PyObject* PyObject_GenericGetAttr(PyObject *o, PyObject *name)
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
:attr:`__dict__` (if present). As outlined in :ref:`descriptors`, data
descriptors take preference over instance attributes, while non-data
descriptors don't. Otherwise, an :exc:`AttributeError` is raised.
.. 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_GenericSetAttr(PyObject *o, PyObject *name, PyObject *value)
Generic attribute setter 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 the attribute in the instance dictionary. Otherwise, the
attribute is set in the object's :attr:`__dict__` (if present). Otherwise,
an :exc:`AttributeError` is raised and ``-1`` is returned.
.. 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)``.
.. versionchanged:: 2.5
These functions returned an :ctype:`int` type. This might require
changes in your code for properly supporting 64-bit systems.
.. 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.
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