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# 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_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.

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.

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)
  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. Returns `-1` on failure. This is the equivalent of the Python statement `o.attr_name = v`.

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`.

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 `__dict__` (if present). 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_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.

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_Bytes`(PyObject *o)

  Compute a bytes representation of object o. In 2.x, this is just a alias for `PyObject_Str()`.

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 `unicode(o)`. Called by the `unicode()` built-in function.

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, `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 `__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.

  Changed in version 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 `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 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.

  New in version 2.1.

  Changed in version 2.3: Older versions of Python did not support a tuple as the second argument.

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_object, PyObject *args, PyObject *kw)
  Return value: New reference.

  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)`.

  New in version 2.2.

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

PyObject* `PyObject_CallMethod`(PyObject *o, char *method, char *format, ...)
  Return value: New reference.

  Call the method named method of object o 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 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 `PyObject *` args, `PyObject_CallMethodObjArgs()` is a faster alternative.

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.

long `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)`.

long `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.

  New in version 2.6.

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.

  New in version 2.2.

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

  Changed in version 2.5: These functions returned an `int` type. This might require changes in your code for properly supporting 64-bit systems.

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)
  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.

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