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# Capsules

Refer to Providing a C API for an Extension Module for more information on using these objects.

`PyCapsule`

  This subtype of `PyObject` represents an opaque value, useful for C extension modules who need to pass an opaque value (as a `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.

`PyCapsule_Destructor`

  The type of a destructor callback for a capsule. Defined as:

      typedef void (*PyCapsule_Destructor)(PyObject *);

  See `PyCapsule_New()` for the semantics of PyCapsule_Destructor callbacks.

int `PyCapsule_CheckExact`(PyObject *p)

  Return true if its argument is a `PyCapsule`.

PyObject* `PyCapsule_New`(void *pointer, const char *name, PyCapsule_Destructor destructor)
  Return value: New reference.

  Create a `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 `PyCapsule_Import()`.

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 `strcmp()` to compare capsule names.

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 `PyCapsule_IsValid()` or `PyErr_Occurred()` to disambiguate.

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 `PyCapsule_IsValid()` or `PyErr_Occurred()` to disambiguate.

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 `PyCapsule_IsValid()` or `PyErr_Occurred()` to disambiguate.

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 `PyImport_ImportModuleNoBlock()`). If no_block is false, import the module conventionally (using `PyImport_ImportModule()`).

  Return the capsule’s internal pointer on success. On failure, set an exception and return NULL. However, if `PyCapsule_Import()` failed to import the module, and no_block was true, no exception is set.

int `PyCapsule_IsValid`(PyObject *capsule, const char *name)

  Determines whether or not capsule is a valid capsule. A valid capsule is non-NULL, passes `PyCapsule_CheckExact()`, has a non-NULL pointer stored in it, and its internal name matches the name parameter. (See `PyCapsule_GetPointer()` for information on how capsule names are compared.)

  In other words, if `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.

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.

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.

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.

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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