python_doc_md/Advanced/c-api/capsule.md

Capsules

::: index pair: object; Capsule :::

Refer to using-capsules{.interpreted-text role="ref"} for more information on using these objects.

::: versionadded 3.1 :::

This subtype of PyObject{.interpreted-text role="c:type"} represents an opaque value, useful for C extension modules which need to pass an opaque value (as a void*{.interpreted-text role="c:expr"} 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.

The type object corresponding to capsule objects. This is the same object as types.CapsuleType{.interpreted-text role="class"} in the Python layer.

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

typedef void (*PyCapsule_Destructor)(PyObject *);

See PyCapsule_New{.interpreted-text role="c:func"} for the semantics of PyCapsule_Destructor callbacks.

Return true if its argument is a PyCapsule{.interpreted-text role="c:type"}. This function always succeeds.

Create a PyCapsule{.interpreted-text role="c:type"} 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{.interpreted-text role="c:func"}.

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{.interpreted-text role="c:func"} to compare capsule names.

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{.interpreted-text role="c:func"} or PyErr_Occurred{.interpreted-text role="c:func"} to disambiguate.

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{.interpreted-text role="c:func"} or PyErr_Occurred{.interpreted-text role="c:func"} to disambiguate.

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{.interpreted-text role="c:func"} or PyErr_Occurred{.interpreted-text role="c:func"} to disambiguate.

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.

This function splits name on the . character, and imports the first element. It then processes further elements using attribute lookups.

Return the capsule's internal pointer on success. On failure, set an exception and return NULL.

:::: note ::: title Note :::

If name points to an attribute of some submodule or subpackage, this submodule or subpackage must be previously imported using other means (for example, by using PyImport_ImportModule{.interpreted-text role="c:func"}) for the attribute lookups to succeed. ::::

::: versionchanged 3.3 no_block has no effect anymore. :::

Determines whether or not capsule is a valid capsule. A valid capsule is non-NULL, passes PyCapsule_CheckExact{.interpreted-text role="c:func"}, has a non-NULL pointer stored in it, and its internal name matches the name parameter. (See PyCapsule_GetPointer{.interpreted-text role="c:func"} for information on how capsule names are compared.)

In other words, if PyCapsule_IsValid{.interpreted-text role="c:func"} 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.

Set the context pointer inside capsule to context.

Return 0 on success. Return nonzero and set an exception on failure.

Set the destructor inside capsule to destructor.

Return 0 on success. Return nonzero and set an exception on failure.

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.

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.