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