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.. 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.
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