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.. _special-functions:
Special functions
-----------------
.. _sequence-protocol:
Sequence Protocol
^^^^^^^^^^^^^^^^^
Support for the sequence protocol is achieved adding functions with special
names, this is done using the :ref:`add-function` tag.
The special function names are:
============= =============================================== ==================== ===================
Function name Parameters Return type CPython equivalent
============= =============================================== ==================== ===================
__len__ PyObject* self Py_ssize_t PySequence_Size
__getitem__ PyObject* self, Py_ssize_t _i PyObject* PySequence_GetItem
__setitem__ PyObject* self, Py_ssize_t _i, PyObject* _value int PySequence_SetItem
__contains__ PyObject* self, PyObject* _value int PySequence_Contains
__concat__ PyObject* self, PyObject* _other PyObject* PySequence_Concat
============= =============================================== ==================== ===================
You just need to inform the function name to the :ref:`add-function` tag, without any
parameter or return type information, when you do it, |project| will create a C
function with parameters and return type defined by the table above.
The function needs to follow the same semantics of the *CPython equivalent*
function, the only way to do it is using the
:ref:`inject-code <codeinjectionsemantics>` tag.
A concrete example how to add sequence protocol support to a class can be found
on shiboken tests, more precisely in the definition of the Str class in
``tests/samplebinding/typesystem_sample.xml``.
.. _bool-cast:
Bool Cast
^^^^^^^^^
Implementing bool casts enables using values which have a concept of validity
in boolean expressions. In C++, this is commonly implemented as
``operator bool() const``. In Qt, relevant classes have a
``bool isNull() const`` function.
In Python, the function ``__bool__`` is used for this. shiboken can generate
this functions depending on the command line options
:ref:`--use-operator-bool-as-nb-bool <use-operator-bool-as-nb-bool>`
and :ref:`--use-isnull-as-nb-bool <use-isnull-as-nb-bool>`,
which can be overridden by specifying the boolean attributes
**isNull** or **operator-bool** on the :ref:`value-type` or :ref:`object-type`
elements in typesystem XML.
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