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Diffstat (limited to 'Doc/howto')
| -rw-r--r-- | Doc/howto/clinic.rst | 50 |
1 files changed, 26 insertions, 24 deletions
diff --git a/Doc/howto/clinic.rst b/Doc/howto/clinic.rst index 9c9a4f4..dcede13 100644 --- a/Doc/howto/clinic.rst +++ b/Doc/howto/clinic.rst @@ -1343,35 +1343,37 @@ state. Example from the ``setattro`` slot method in See also :pep:`573`. +.. _clinic-howto-custom-converter: + How to write a custom converter ------------------------------- -As we hinted at in the previous section... you can write your own converters! -A converter is simply a Python class that inherits from :py:class:`!CConverter`. -The main purpose of a custom converter is if you have a parameter using -the ``O&`` format unit—parsing this parameter means calling +A converter is a Python class that inherits from :py:class:`!CConverter`. +The main purpose of a custom converter, is for parameters parsed with +the ``O&`` format unit --- parsing such a parameter means calling a :c:func:`PyArg_ParseTuple` "converter function". -Your converter class should be named ``*something*_converter``. -If the name follows this convention, then your converter class -will be automatically registered with Argument Clinic; its name -will be the name of your class with the ``_converter`` suffix -stripped off. (This is accomplished with a metaclass.) - -You shouldn't subclass :py:meth:`!CConverter.__init__`. Instead, you should -write a :py:meth:`!converter_init` function. :py:meth:`!converter_init` -always accepts a *self* parameter; after that, all additional -parameters *must* be keyword-only. Any arguments passed in to -the converter in Argument Clinic will be passed along to your -:py:meth:`!converter_init`. +Your converter class should be named :samp:`{ConverterName}_converter`. +By following this convention, your converter class will be automatically +registered with Argument Clinic, with its *converter name* being the name of +your converter class with the ``_converter`` suffix stripped off. -There are some additional members of :py:class:`!CConverter` you may wish -to specify in your subclass. Here's the current list: +Instead of subclassing :py:meth:`!CConverter.__init__`, +write a :py:meth:`!converter_init` method. +Apart for the *self* parameter, all additional :py:meth:`!converter_init` +parameters **must** be keyword-only. +Any arguments passed to the converter in Argument Clinic +will be passed along to your :py:meth:`!converter_init` method. +See :py:class:`!CConverter` for a list of members you may wish to specify in +your subclass. .. module:: clinic .. class:: CConverter + The base class for all converters. + See :ref:`clinic-howto-custom-converter` for how to subclass this class. + .. attribute:: type The C type to use for this variable. @@ -1436,16 +1438,16 @@ Here's the simplest example of a custom converter, from :source:`Modules/zlibmod [python start generated code]*/ /*[python end generated code: output=da39a3ee5e6b4b0d input=35521e4e733823c7]*/ -This block adds a converter to Argument Clinic named ``ssize_t``. Parameters -declared as ``ssize_t`` will be declared as type :c:type:`Py_ssize_t`, and will -be parsed by the ``'O&'`` format unit, which will call the -``ssize_t_converter`` converter function. ``ssize_t`` variables -automatically support default values. +This block adds a converter named ``ssize_t`` to Argument Clinic. +Parameters declared as ``ssize_t`` will be declared with type :c:type:`Py_ssize_t`, +and will be parsed by the ``'O&'`` format unit, +which will call the :c:func:`!ssize_t_converter` converter C function. +``ssize_t`` variables automatically support default values. More sophisticated custom converters can insert custom C code to handle initialization and cleanup. You can see more examples of custom converters in the CPython -source tree; grep the C files for the string :py:class:`!CConverter`. +source tree; grep the C files for the string ``CConverter``. How to write a custom return converter |