.. highlight:: c
.. _capsules:
Capsules
--------
.. index:: pair: object; Capsule
Refer to :ref:`using-capsules` for more information on using these objects.
.. versionadded:: 3.1
.. c:type:: PyCapsule
This subtype of :c:type:`PyObject` represents an opaque value, useful for C
extension modules who need to pass an opaque value (as a :c:expr:`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.
.. c:type:: PyCapsule_Destructor
The type of a destructor callback for a capsule. Defined as::
typedef void (*PyCapsule_Destructor)(PyObject *);
See :c:func:`PyCapsule_New` for the semantics of PyCapsule_Destructor
callbacks.
.. c:function:: int PyCapsule_CheckExact(PyObject *p)
Return true if its argument is a :c:type:`PyCapsule`. This function always
succeeds.
.. c:function:: PyObject* PyCapsule_New(void *pointer, const char *name, PyCapsule_Destructor destructor)
Create a :c:type:`PyCapsule` encapsulating the *pointer*. The *pointer*
argument may not be ``NULL``.
On failure, set an exception and return ``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 as its argument when it is destroyed.
If this capsule will be stored as an attribute of a module, the *name* should
be specified as ``modulename.attributename``. This will enable other modules
to import the capsule using :c:func:`PyCapsule_Import`.
.. c:function:: void* PyCapsule_GetPointer(PyObject *capsule, const char *name)
Retrieve the *pointer* stored in the capsule. On failure, set an exception
and return ``NULL``.
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``. Python uses the C function :c:func:`!strcmp` to compare capsule
names.
.. c:function:: 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 :c:func:`PyCapsule_IsValid` or
:c:func:`PyErr_Occurred` to disambiguate.
.. c:function:: 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 :c:func:`PyCapsule_IsValid` or
:c:func:`PyErr_Occurred` to disambiguate.
.. c:function:: 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 :c:func:`PyCapsule_IsValid` or
:c:func:`PyErr_Occurred` to disambiguate.
.. c:function:: 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.
Return the capsule's internal *pointer* on success. On failure, set an
exception and return ``NULL``.
.. versionchanged:: 3.3
*no_block* has no effect anymore.
.. c:function:: int PyCapsule_IsValid(PyObject *capsule, const char *name)
Determines whether or not *capsule* is a valid capsule. A valid capsule is
non-``NULL``, passes :c:func:`PyCapsule_CheckExact`, has a non-``NULL`` pointer
stored in it, and its internal name matches the *name* parameter. (See
:c:func:`PyCapsule_GetPointer` for information on how capsule names are
compared.)
In other words, if :c:func:`PyCapsule_IsValid` returns a true value, calls to
any of the accessors (any function starting with ``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.
.. c:function:: 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.
.. c:function:: int PyCapsule_SetDestructor(PyObject *capsule, PyCapsule_Destructor destructor)
Set the destructor inside *capsule* to *destructor*.
Return ``0`` on success. Return nonzero and set an exception on failure.
.. c:function:: 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.
.. c:function:: 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.
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