Python/C API Reference Manual

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6.1 Object Protocol

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_HasAttrString(PyObject *o, 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.

PyObject* PyObject_GetAttrString(PyObject *o, 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".

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.

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".

int PyObject_SetAttrString(PyObject *o, 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".

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".

int PyObject_DelAttrString(PyObject *o, 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".

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_Cmp(PyObject *o1, PyObject *o2, int *result)

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)".

int PyObject_Compare(PyObject *o1, PyObject *o2)

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 PyErr_Occurred() to detect an error. This is equivalent to the Python expression "cmp(o1, o2)".

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 and by reverse quotes.

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 by the print statement.

PyObject* PyObject_Unicode(PyObject *o)

Return value: New reference.

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 "unistr(o)". Called by the unistr() built-in function.

int PyObject_IsInstance(PyObject *inst, PyObject *cls)

Return 1 if inst is an instance of the class cls or a subclass of cls. If cls is a type object rather than a class object, PyObject_IsInstance() returns 1 if inst is of type cls. If inst is not a class instance and cls is neither a type object or class object, inst must have a __class__ attribute -- the class relationship of the value of that attribute with cls will be used to determine the result of this function. New in version 2.1.

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 A and B are class objects, B is a subclass of A if it inherits from 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, PyObject_IsSubclass() returns true. If A and B are different objects, B's __bases__ attribute is searched in a depth-first fashion for A -- the presence of the __bases__ attribute is considered sufficient for this determination.

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 either derived or cls is not an actual class object, this function uses the generic algorithm described above. New in version 2.1.

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_CallObject(PyObject *callable_object, PyObject *args)

Return value: New reference.

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)".

PyObject* PyObject_CallFunction(PyObject *callable, 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 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)".

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

Return value: New reference.

Call the method named m of object o with a variable number of C arguments. The C arguments are described by a Py_BuildValue() 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 "o.method(args)".

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. Returns the result of the call on success, or NULL on failure. New in version 2.2.

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

Return value: New reference.

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 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. New in version 2.2.

int 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)". 

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". This function always succeeds.

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).

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. New in version 2.2.

int PyObject_Length(PyObject *o)

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

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. Returns -1 on failure. This is the equivalent of the Python statement "o[key] = v".

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]".

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 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.

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)

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.

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Python/C API Reference Manual

Previous: 6. Abstract Objects Layer Up: 6. Abstract Objects Layer Next: 6.2 Number Protocol

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Release 2.2.1, documentation updated on April 10, 2002.