Edit File: capsule.txt
.. highlightlang:: c .. _capsules: Capsules -------- .. index:: object: Capsule Refer to :ref:`using-capsules` for more information on using these objects. .. 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:type:`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`. .. 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. If *no_block* is true, import the module without blocking (using :c:func:`PyImport_ImportModuleNoBlock`). If *no_block* is false, import the module conventionally (using :c:func:`PyImport_ImportModule`). Return the capsule's internal *pointer* on success. On failure, set an exception and return *NULL*. However, if :c:func:`PyCapsule_Import` failed to import the module, and *no_block* was true, no exception is set. .. 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 :c:func:`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.