add a replacement API for PyCObject, PyCapsule #5630

All stdlib modules with C-APIs now use this.

Patch by Larry Hastings

Doc/c-api/capsule.rst

@@ -0,0 +1,168 @@
+.. highlightlang:: c
+
+.. _capsules:
+
+Capsules
+--------
+
+.. index:: object: Capsule
+
+Refer to :ref:`using-capsules` for more information on using these objects.
+
+
+.. ctype:: PyCapsule
+
+   This subtype of :ctype:`PyObject` represents an opaque value, useful for C
+   extension modules who need to pass an opaque value (as a :ctype:`void\*`
+   pointer) through Python code to other C code.  It is often used to make a C
+   function pointer defined in one module available to other modules, so the
+   regular import mechanism can be used to access C APIs defined in dynamically
+   loaded modules.
+
+.. ctype:: PyCapsule_Destructor
+
+   The type of a destructor callback for a capsule.  Defined as::
+
+      typedef void (*PyCapsule_Destructor)(PyObject *);
+
+   See :cfunc:`PyCapsule_New` for the semantics of PyCapsule_Destructor
+   callbacks.
+
+
+.. cfunction:: int PyCapsule_CheckExact(PyObject *p)
+
+   Return true if its argument is a :ctype:`PyCapsule`.
+
+.. cfunction:: PyObject* PyCapsule_New(void* pointer, const char* name, PyCapsule_Destructor destructor)
+
+   Create a :ctype:`PyCapsule` encapsulating the *pointer*.  The *pointer*
+   argument may not be *NULL*.
+
+   The *name* string may either be *NULL* or a pointer to a valid
+   C string.  If non-*NULL*, this string must outlive the capsule.
+   (Though it is permitted to free it inside the *destructor*.)
+
+   If the *destructor* argument is not *NULL*,
+   it will be called with the capsule ``PyObject *`` when it is destroyed.
+
+   If this capsule will be stored as an attribute of a module, it
+   is strongly suggested that the *name* string be specified as::
+
+      modulename.attributename
+
+   This will enable other modules to import the capsule
+   using :cfunc:`PyCapsule_Import`.
+
+   Return a valid capsule on success.
+   On failure, set an exception and return *NULL*.
+
+
+.. cfunction:: void* PyCapsule_GetPointer(PyObject* capsule, const char* name)
+
+   Retrieve the *pointer* stored in the capsule.
+
+   The *name* parameter must compare exactly to the name stored in the capsule.
+   If the name stored in the capsule is *NULL*, the *name* passed in must
+   also be *NULL*.  If the name stored in the capsule is non-*NULL*,
+   the *name* passed in must also be non-*NULL*, and must match the name
+   stored in the capsule.  Python uses the C function *strcmp* to compare
+   capsule names.
+
+   Return the internal *pointer* on success.
+   On failure, set an exception and return *NULL*.
+
+
+.. cfunction:: PyCapsule_Destructor PyCapsule_GetDestructor(PyObject* capsule)
+
+   Return the current *destructor* stored in the capsule.
+   On failure, set an exception and return *NULL*.
+
+   It is legal for a capsule to have a *NULL* destructor.
+   This makes a *NULL* return code somewhat ambiguous;
+   use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate.
+
+
+.. cfunction:: void* PyCapsule_GetContext(PyObject* capsule)
+
+   Return the current *context* stored in the capsule.
+   On failure, set an exception and return *NULL*.
+
+   It is legal for a capsule to have a *NULL* context.
+   This makes a *NULL* return code somewhat ambiguous;
+   use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate.
+
+
+.. cfunction:: const char* PyCapsule_GetName(PyObject* capsule)
+
+   Return the current *name* stored in the capsule.
+   On failure, set an exception and return *NULL*.
+
+   It is legal for a capsule to have a *NULL* name.
+   This makes a *NULL* return code somewhat ambiguous;
+   use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate.
+
+
+.. cfunction:: void* PyCapsule_Import(const char* name, int no_block)
+
+   Import a pointer to a C object from a ``capsule`` attribute in a module.
+   The *name* parameter should specify the full name to the attribute, as
+   in *"module.attribute"*.
+   The *name* stored in the capsule must match this string exactly.
+   If *no_block* is true, import the module without blocking
+   (using :cfunc:`PyImport_ImportModuleNoBlock`).
+   If *no_block* is false, import the module conventionally
+   (using :cfunc:`PyImport_ImportModule`).
+
+   Return the capsule's internal *pointer* on success.
+   On failure, set an exception and return *NULL*.
+   Exception: if *PyCapsule_Import* failed to import the module,
+   and *no_block* was true, no exception is set.
+
+.. cfunction:: int PyCapsule_IsValid(PyObject* capsule, const char* name)
+
+   Determines whether or not a :ctype:`PyObject \*` is a valid capsule.
+   A valid capsule is non-*NULL*, passes :cfunc:`PyCapsule_CheckExact`,
+   has a non-NULL *pointer*, and its internal name matches the
+   *name* parameter.  (See :cfunc:`PyCapsule_GetPointer` for
+   information on how capsule names are compared.)
+
+   In other words, if :cfunc:`PyCapsule_IsValid` returns a true value,
+   calls to any of the accessors (any function starting
+   with :cfunc:`PyCapsule_Get`) are guaranteed to succeed.
+
+   Return a nonzero value if the object is valid and matches the name
+   passed in.
+   Return 0 otherwise.
+   This function will not fail.
+
+.. cfunction:: int PyCapsule_SetContext(PyObject* capsule, void* context)
+
+   Set the context pointer inside *capsule* to *context*.
+
+   Return 0 on success.
+   Return nonzero and set an exception on failure.
+
+.. cfunction:: int PyCapsule_SetDestructor(PyObject* capsule, void (*)(PyObject *) destructor)
+
+   Set the destructor inside *capsule* to *destructor*.
+
+   Return 0 on success.
+   Return nonzero and set an exception on failure.
+
+.. cfunction:: int PyCapsule_SetName(PyObject* capsule, const char* name)
+
+   Set the name inside *capsule* to *name*.  If non-*NULL*, the name
+   must outlive the capsule.  If the previous *name* stored in the
+   capsule was not *NULL*, no attempt is made to free it.
+
+   Return 0 on success.
+   Return nonzero and set an exception on failure.
+
+.. cfunction:: int PyCapsule_SetPointer(PyObject* capsule, void* pointer)
+
+   Set the void pointer inside *capsule* to *pointer*.  The pointer
+   may not be *NULL*.
+
+   Return 0 on success.
+   Return nonzero and set an exception on failure.
+