Issue #20214: Fixed a number of small issues and documentation errors in

Argument Clinic (see issue for details). GitHub-Issue-Link: python/cpython#64413
python · erlend-aasland · Sep 26, 2023 · Jan 4, 2014 · Jan 5, 2014 · Jan 7, 2014
commit 5c53fd963b84ea38608a59656675c189f6206a35
diff --git a/Doc/howto/clinic.rst b/Doc/howto/clinic.rst
@@ -109,6 +109,13 @@ convert a function to work with it.  Let's dive in!
    support all of these scenarios.  But these are advanced
    topics--let's do something simpler for your first function.
 
+   Also, if the function has multiple calls to :c:func:`PyArg_ParseTuple`
+   or :c:func:`PyArg_ParseTupleAndKeywords` where it supports different
+   types for the same argument, or if the function uses something besides
+   PyArg_Parse functions to parse its arguments, it probably
+   isn't suitable for conversion to Argument Clinic.  Argument Clinic
+   doesn't support generic functions or polymorphic parameters.
+
 3. Add the following boilerplate above the function, creating our block::
 
     /*[clinic input]
@@ -170,6 +177,11 @@ convert a function to work with it.  Let's dive in!
     Write a pickled representation of obj to the open file.
     [clinic start generated code]*/
 
+   The name of the class and module should be the same as the one
+   seen by Python.  Check the name defined in the :c:type:`PyModuleDef`
+   or :c:type:`PyTypeObject` as appropriate.
+
+
 
 8. Declare each of the parameters to the function.  Each parameter
    should get its own line.  All the parameter lines should be
@@ -455,6 +467,28 @@ convert a function to work with it.  Let's dive in!
 Advanced Topics
 ===============
 
+Now that you've had some experience working with Argument Clinic, it's time
+for some advanced topics.
+
+
+Symbolic default values
+-----------------------
+
+The default value you provide for a parameter can't be any arbitrary
+expression.  Currently the following are explicitly supported:
+
+* Numeric constants (integer and float)
+* String constants
+* ``True``, ``False``, and ``None``
+* Simple symbolic constants like ``sys.maxsize``, which must
+  start with the name of the module
+
+In case you're curious, this is implemented in  ``from_builtin()``
+in ``Lib/inspect.py``.
+
+(In the future, this may need to get even more elaborate,
+to allow full expressions like ``CONSTANT - 1``.)
+
 
 Renaming the C functions generated by Argument Clinic
 -----------------------------------------------------
@@ -479,6 +513,29 @@ The base function would now be named ``pickler_dumper()``,
 and the impl function would now be named ``pickler_dumper_impl()``.
 
 
+The NULL default value
+----------------------
+
+For string and object parameters, you can set them to ``None`` to indicate
+that there is no default.  However, that means the C variable will be
+initialized to ``Py_None``.  For convenience's sakes, there's a special
+value called ``NULL`` for just this case: from Python's perspective it
+behaves like a default value of ``None``, but the C variable is initialized
+with ``NULL``.
+
+
+Converting functions using PyArg_UnpackTuple
+--------------------------------------------
+
+To convert a function parsing its arguments with :c:func:`PyArg_UnpackTuple`,
+simply write out all the arguments, specifying each as an ``object``.  You
+may specify the ``type`` argument to cast the type as appropriate.  All
+arguments should be marked positional-only (add a ``/`` on a line by itself
+after the last argument).
+
+Currently the generated code will use :c:func:`PyArg_ParseTuple`, but this
+will change soon.
+
 Optional Groups
 ---------------
 
@@ -570,8 +627,8 @@ To save time, and to minimize how much you need to learn
 to achieve your first port to Argument Clinic, the walkthrough above tells
 you to use "legacy converters".  "Legacy converters" are a convenience,
 designed explicitly to make porting existing code to Argument Clinic
-easier.  And to be clear, their use is entirely acceptable when porting
-code for Python 3.4.
+easier.  And to be clear, their use is acceptable when porting code for
+Python 3.4.
 
 However, in the long term we probably want all our blocks to
 use Argument Clinic's real syntax for converters.  Why?  A couple
@@ -585,8 +642,8 @@ reasons:
   restricted to what :c:func:`PyArg_ParseTuple` supports; this flexibility
   won't be available to parameters using legacy converters.
 
-Therefore, if you don't mind a little extra effort, you should consider
-using normal converters instead of legacy converters.
+Therefore, if you don't mind a little extra effort, please use the normal
+converters instead of legacy converters.
 
 In a nutshell, the syntax for Argument Clinic (non-legacy) converters
 looks like a Python function call.  However, if there are no explicit
@@ -597,12 +654,19 @@ the same converters.
 All arguments to Argument Clinic converters are keyword-only.
 All Argument Clinic converters accept the following arguments:
 
-``doc_default``
-  If the parameter takes a default value, normally this value is also
-  provided in the ``inspect.Signature`` metadata, and displayed in the
-  docstring.  ``doc_default`` lets you override the value used in these
-  two places: pass in a string representing the Python value you wish
-  to use in these two contexts.
+``py_default``
+  The default value for this parameter when defined in Python.
+  Specifically, the value that will be used in the ``inspect.Signature``
+  string.
+  If a default value is specified for the parameter, defaults to
+  ``repr(default)``, else defaults to ``None``.
+  Specified as a string.
+
+``c_default``
+  The default value for this parameter when defined in C.
+  Specifically, this will be the initializer for the variable declared
+  in the "parse function".
+  Specified as a string.
 
 ``required``
   If a parameter takes a default value, Argument Clinic infers that the
@@ -612,6 +676,9 @@ All Argument Clinic converters accept the following arguments:
   Clinic that this parameter is not optional, even if it has a default
   value.
 
+  (The need for ``required`` may be obviated by ``c_default``, which is
+  newer but arguably a better solution.)
+
 ``annotation``
   The annotation value for this parameter.  Not currently supported,
   because PEP 8 mandates that the Python library may not use
@@ -634,10 +701,11 @@ on the right is the text you'd replace it with.
 ``'et'``    ``str(encoding='name_of_encoding', types='bytes bytearray str')``
 ``'f'``     ``float``
 ``'h'``     ``short``
-``'H'``     ``unsigned_short``
+``'H'``     ``unsigned_short(bitwise=True)``
 ``'i'``     ``int``
-``'I'``     ``unsigned_int``
-``'K'``     ``unsigned_PY_LONG_LONG``
+``'I'``     ``unsigned_int(bitwise=True)``
+``'k'``     ``unsigned_long(bitwise=True)``
+``'K'``     ``unsigned_PY_LONG_LONG(bitwise=True)``
 ``'L'``     ``PY_LONG_LONG``
 ``'n'``     ``Py_ssize_t``
 ``'O!'``    ``object(subclass_of='&PySomething_Type')``
@@ -681,6 +749,14 @@ available.  For each converter it'll show you all the parameters
 it accepts, along with the default value for each parameter.
 Just run ``Tools/clinic/clinic.py --converters`` to see the full list.
 
+Py_buffer
+---------
+
+When using the ``Py_buffer`` converter
+(or the ``'s*'``, ``'w*'``, ``'*y'``, or ``'z*'`` legacy converters)
+note that the code Argument Clinic generates for you will automatically
+call :c:func:`PyBuffer_Release` on the buffer for you.
+
 
 Advanced converters
 -------------------
@@ -745,15 +821,26 @@ encode the value you return like normal.
 
 Currently Argument Clinic supports only a few return converters::
 
+    bool
     int
+    unsigned int
     long
+    unsigned int
+    size_t
     Py_ssize_t
+    float
+    double
     DecodeFSDefault
 
 None of these take parameters.  For the first three, return -1 to indicate
 error.  For ``DecodeFSDefault``, the return type is ``char *``; return a NULL
 pointer to indicate an error.
 
+(There's also an experimental ``NoneType`` converter, which lets you
+return ``Py_None`` on success or ``NULL`` on failure, without having
+to increment the reference count on ``Py_None``.  I'm not sure it adds
+enough clarity to be worth using.)
+
 To see all the return converters Argument Clinic supports, along with
 their parameters (if any),
 just run ``Tools/clinic/clinic.py --converters`` for the full list.
@@ -873,13 +960,6 @@ to specify in your subclass.  Here's the current list:
     The Python default value for this parameter, as a Python value.
     Or the magic value ``unspecified`` if there is no default.
 
-``doc_default``
-    ``default`` as it should appear in the documentation,
-    as a string.
-    Or ``None`` if there is no default.
-    This string, when run through ``eval()``, should produce
-    a Python value.
-
 ``py_default``
     ``default`` as it should appear in Python code,
     as a string.
@@ -951,6 +1031,26 @@ write your own return converter, please read ``Tools/clinic/clinic.py``,
 specifically the implementation of ``CReturnConverter`` and
 all its subclasses.
 
+METH_O and METH_NOARGS
+----------------------------------------------
+
+To convert a function using ``METH_O``, make sure the function's
+single argument is using the ``object`` converter, and mark the
+arguments as positional-only::
+
+    /*[clinic input]
+    meth_o_sample
+
+         argument: object
+         /
+    [clinic start generated code]*/
+
+
+To convert a function using ``METH_NOARGS``, just don't specify
+any arguments.
+
+You can still use a self converter, a return converter, and specify
+a ``type`` argument to the object converter for ``METH_O``.
 
 Using Argument Clinic in Python files
 -------------------------------------