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Issue #20214: Fixed a number of small issues and documentation errors in
Argument Clinic (see issue for details).
This commit is contained in:
Larry Hastings
parent
583baa8fef
commit
4a55fc5a9d
4 changed files with 223 additions and 50 deletions
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@ -109,6 +109,13 @@ convert a function to work with it. Let's dive in!
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support all of these scenarios. But these are advanced
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topics--let's do something simpler for your first function.
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Also, if the function has multiple calls to :c:func:`PyArg_ParseTuple`
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or :c:func:`PyArg_ParseTupleAndKeywords` where it supports different
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types for the same argument, or if the function uses something besides
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PyArg_Parse functions to parse its arguments, it probably
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isn't suitable for conversion to Argument Clinic. Argument Clinic
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doesn't support generic functions or polymorphic parameters.
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3. Add the following boilerplate above the function, creating our block::
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/*[clinic input]
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@ -170,6 +177,11 @@ convert a function to work with it. Let's dive in!
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Write a pickled representation of obj to the open file.
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[clinic start generated code]*/
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The name of the class and module should be the same as the one
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seen by Python. Check the name defined in the :c:type:`PyModuleDef`
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or :c:type:`PyTypeObject` as appropriate.
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8. Declare each of the parameters to the function. Each parameter
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should get its own line. All the parameter lines should be
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@ -455,6 +467,28 @@ convert a function to work with it. Let's dive in!
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Advanced Topics
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===============
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Now that you've had some experience working with Argument Clinic, it's time
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for some advanced topics.
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Symbolic default values
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-----------------------
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The default value you provide for a parameter can't be any arbitrary
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expression. Currently the following are explicitly supported:
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* Numeric constants (integer and float)
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* String constants
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* ``True``, ``False``, and ``None``
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* Simple symbolic constants like ``sys.maxsize``, which must
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start with the name of the module
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In case you're curious, this is implemented in ``from_builtin()``
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in ``Lib/inspect.py``.
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(In the future, this may need to get even more elaborate,
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to allow full expressions like ``CONSTANT - 1``.)
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Renaming the C functions generated by Argument Clinic
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-----------------------------------------------------
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@ -479,6 +513,29 @@ The base function would now be named ``pickler_dumper()``,
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and the impl function would now be named ``pickler_dumper_impl()``.
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The NULL default value
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----------------------
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For string and object parameters, you can set them to ``None`` to indicate
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that there is no default. However, that means the C variable will be
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initialized to ``Py_None``. For convenience's sakes, there's a special
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value called ``NULL`` for just this case: from Python's perspective it
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behaves like a default value of ``None``, but the C variable is initialized
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with ``NULL``.
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Converting functions using PyArg_UnpackTuple
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--------------------------------------------
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To convert a function parsing its arguments with :c:func:`PyArg_UnpackTuple`,
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simply write out all the arguments, specifying each as an ``object``. You
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may specify the ``type`` argument to cast the type as appropriate. All
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arguments should be marked positional-only (add a ``/`` on a line by itself
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after the last argument).
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Currently the generated code will use :c:func:`PyArg_ParseTuple`, but this
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will change soon.
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Optional Groups
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---------------
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@ -570,8 +627,8 @@ To save time, and to minimize how much you need to learn
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to achieve your first port to Argument Clinic, the walkthrough above tells
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you to use "legacy converters". "Legacy converters" are a convenience,
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designed explicitly to make porting existing code to Argument Clinic
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easier. And to be clear, their use is entirely acceptable when porting
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code for Python 3.4.
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easier. And to be clear, their use is acceptable when porting code for
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Python 3.4.
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However, in the long term we probably want all our blocks to
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use Argument Clinic's real syntax for converters. Why? A couple
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@ -585,8 +642,8 @@ reasons:
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restricted to what :c:func:`PyArg_ParseTuple` supports; this flexibility
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won't be available to parameters using legacy converters.
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Therefore, if you don't mind a little extra effort, you should consider
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using normal converters instead of legacy converters.
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Therefore, if you don't mind a little extra effort, please use the normal
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converters instead of legacy converters.
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In a nutshell, the syntax for Argument Clinic (non-legacy) converters
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looks like a Python function call. However, if there are no explicit
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@ -597,12 +654,19 @@ the same converters.
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All arguments to Argument Clinic converters are keyword-only.
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All Argument Clinic converters accept the following arguments:
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``doc_default``
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If the parameter takes a default value, normally this value is also
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provided in the ``inspect.Signature`` metadata, and displayed in the
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docstring. ``doc_default`` lets you override the value used in these
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two places: pass in a string representing the Python value you wish
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to use in these two contexts.
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``py_default``
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The default value for this parameter when defined in Python.
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Specifically, the value that will be used in the ``inspect.Signature``
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string.
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If a default value is specified for the parameter, defaults to
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``repr(default)``, else defaults to ``None``.
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Specified as a string.
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``c_default``
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The default value for this parameter when defined in C.
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Specifically, this will be the initializer for the variable declared
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in the "parse function".
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Specified as a string.
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``required``
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If a parameter takes a default value, Argument Clinic infers that the
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@ -612,6 +676,9 @@ All Argument Clinic converters accept the following arguments:
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Clinic that this parameter is not optional, even if it has a default
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value.
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(The need for ``required`` may be obviated by ``c_default``, which is
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newer but arguably a better solution.)
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``annotation``
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The annotation value for this parameter. Not currently supported,
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because PEP 8 mandates that the Python library may not use
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@ -634,10 +701,11 @@ on the right is the text you'd replace it with.
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``'et'`` ``str(encoding='name_of_encoding', types='bytes bytearray str')``
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``'f'`` ``float``
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``'h'`` ``short``
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``'H'`` ``unsigned_short``
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``'H'`` ``unsigned_short(bitwise=True)``
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``'i'`` ``int``
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``'I'`` ``unsigned_int``
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``'K'`` ``unsigned_PY_LONG_LONG``
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``'I'`` ``unsigned_int(bitwise=True)``
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``'k'`` ``unsigned_long(bitwise=True)``
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``'K'`` ``unsigned_PY_LONG_LONG(bitwise=True)``
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``'L'`` ``PY_LONG_LONG``
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``'n'`` ``Py_ssize_t``
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``'O!'`` ``object(subclass_of='&PySomething_Type')``
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@ -681,6 +749,14 @@ available. For each converter it'll show you all the parameters
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it accepts, along with the default value for each parameter.
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Just run ``Tools/clinic/clinic.py --converters`` to see the full list.
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Py_buffer
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---------
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When using the ``Py_buffer`` converter
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(or the ``'s*'``, ``'w*'``, ``'*y'``, or ``'z*'`` legacy converters)
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note that the code Argument Clinic generates for you will automatically
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call :c:func:`PyBuffer_Release` on the buffer for you.
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Advanced converters
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-------------------
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@ -745,15 +821,26 @@ encode the value you return like normal.
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Currently Argument Clinic supports only a few return converters::
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bool
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int
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unsigned int
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long
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unsigned int
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size_t
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Py_ssize_t
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float
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double
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DecodeFSDefault
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None of these take parameters. For the first three, return -1 to indicate
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error. For ``DecodeFSDefault``, the return type is ``char *``; return a NULL
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pointer to indicate an error.
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(There's also an experimental ``NoneType`` converter, which lets you
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return ``Py_None`` on success or ``NULL`` on failure, without having
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to increment the reference count on ``Py_None``. I'm not sure it adds
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enough clarity to be worth using.)
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To see all the return converters Argument Clinic supports, along with
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their parameters (if any),
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just run ``Tools/clinic/clinic.py --converters`` for the full list.
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@ -873,13 +960,6 @@ to specify in your subclass. Here's the current list:
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The Python default value for this parameter, as a Python value.
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Or the magic value ``unspecified`` if there is no default.
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``doc_default``
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``default`` as it should appear in the documentation,
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as a string.
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Or ``None`` if there is no default.
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This string, when run through ``eval()``, should produce
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a Python value.
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``py_default``
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``default`` as it should appear in Python code,
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as a string.
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@ -951,6 +1031,26 @@ write your own return converter, please read ``Tools/clinic/clinic.py``,
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specifically the implementation of ``CReturnConverter`` and
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all its subclasses.
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METH_O and METH_NOARGS
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----------------------------------------------
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To convert a function using ``METH_O``, make sure the function's
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single argument is using the ``object`` converter, and mark the
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arguments as positional-only::
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/*[clinic input]
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meth_o_sample
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argument: object
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/
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[clinic start generated code]*/
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To convert a function using ``METH_NOARGS``, just don't specify
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any arguments.
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You can still use a self converter, a return converter, and specify
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a ``type`` argument to the object converter for ``METH_O``.
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Using Argument Clinic in Python files
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-------------------------------------
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