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# 8. Sequence Protocol

Support for the sequence protocol is achieved adding functions with special names, this is done using the 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 add-function tag, without any parameter or return type information, when you do it, Shiboken will create a C function with parameters and return type definied 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 inject-code tag.

A concrete exemple 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`.