1.. highlight:: c 2 3.. _capsules: 4 5Capsules 6-------- 7 8.. index:: object: Capsule 9 10Refer to :ref:`using-capsules` for more information on using these objects. 11 12.. versionadded:: 3.1 13 14 15.. c:type:: PyCapsule 16 17 This subtype of :c:type:`PyObject` represents an opaque value, useful for C 18 extension modules who need to pass an opaque value (as a :c:type:`void*` 19 pointer) through Python code to other C code. It is often used to make a C 20 function pointer defined in one module available to other modules, so the 21 regular import mechanism can be used to access C APIs defined in dynamically 22 loaded modules. 23 24 25.. c:type:: PyCapsule_Destructor 26 27 The type of a destructor callback for a capsule. Defined as:: 28 29 typedef void (*PyCapsule_Destructor)(PyObject *); 30 31 See :c:func:`PyCapsule_New` for the semantics of PyCapsule_Destructor 32 callbacks. 33 34 35.. c:function:: int PyCapsule_CheckExact(PyObject *p) 36 37 Return true if its argument is a :c:type:`PyCapsule`. This function always 38 succeeds. 39 40 41.. c:function:: PyObject* PyCapsule_New(void *pointer, const char *name, PyCapsule_Destructor destructor) 42 43 Create a :c:type:`PyCapsule` encapsulating the *pointer*. The *pointer* 44 argument may not be ``NULL``. 45 46 On failure, set an exception and return ``NULL``. 47 48 The *name* string may either be ``NULL`` or a pointer to a valid C string. If 49 non-``NULL``, this string must outlive the capsule. (Though it is permitted to 50 free it inside the *destructor*.) 51 52 If the *destructor* argument is not ``NULL``, it will be called with the 53 capsule as its argument when it is destroyed. 54 55 If this capsule will be stored as an attribute of a module, the *name* should 56 be specified as ``modulename.attributename``. This will enable other modules 57 to import the capsule using :c:func:`PyCapsule_Import`. 58 59 60.. c:function:: void* PyCapsule_GetPointer(PyObject *capsule, const char *name) 61 62 Retrieve the *pointer* stored in the capsule. On failure, set an exception 63 and return ``NULL``. 64 65 The *name* parameter must compare exactly to the name stored in the capsule. 66 If the name stored in the capsule is ``NULL``, the *name* passed in must also 67 be ``NULL``. Python uses the C function :c:func:`strcmp` to compare capsule 68 names. 69 70 71.. c:function:: PyCapsule_Destructor PyCapsule_GetDestructor(PyObject *capsule) 72 73 Return the current destructor stored in the capsule. On failure, set an 74 exception and return ``NULL``. 75 76 It is legal for a capsule to have a ``NULL`` destructor. This makes a ``NULL`` 77 return code somewhat ambiguous; use :c:func:`PyCapsule_IsValid` or 78 :c:func:`PyErr_Occurred` to disambiguate. 79 80 81.. c:function:: void* PyCapsule_GetContext(PyObject *capsule) 82 83 Return the current context stored in the capsule. On failure, set an 84 exception and return ``NULL``. 85 86 It is legal for a capsule to have a ``NULL`` context. This makes a ``NULL`` 87 return code somewhat ambiguous; use :c:func:`PyCapsule_IsValid` or 88 :c:func:`PyErr_Occurred` to disambiguate. 89 90 91.. c:function:: const char* PyCapsule_GetName(PyObject *capsule) 92 93 Return the current name stored in the capsule. On failure, set an exception 94 and return ``NULL``. 95 96 It is legal for a capsule to have a ``NULL`` name. This makes a ``NULL`` return 97 code somewhat ambiguous; use :c:func:`PyCapsule_IsValid` or 98 :c:func:`PyErr_Occurred` to disambiguate. 99 100 101.. c:function:: void* PyCapsule_Import(const char *name, int no_block) 102 103 Import a pointer to a C object from a capsule attribute in a module. The 104 *name* parameter should specify the full name to the attribute, as in 105 ``module.attribute``. The *name* stored in the capsule must match this 106 string exactly. If *no_block* is true, import the module without blocking 107 (using :c:func:`PyImport_ImportModuleNoBlock`). If *no_block* is false, 108 import the module conventionally (using :c:func:`PyImport_ImportModule`). 109 110 Return the capsule's internal *pointer* on success. On failure, set an 111 exception and return ``NULL``. 112 113 114.. c:function:: int PyCapsule_IsValid(PyObject *capsule, const char *name) 115 116 Determines whether or not *capsule* is a valid capsule. A valid capsule is 117 non-``NULL``, passes :c:func:`PyCapsule_CheckExact`, has a non-``NULL`` pointer 118 stored in it, and its internal name matches the *name* parameter. (See 119 :c:func:`PyCapsule_GetPointer` for information on how capsule names are 120 compared.) 121 122 In other words, if :c:func:`PyCapsule_IsValid` returns a true value, calls to 123 any of the accessors (any function starting with :c:func:`PyCapsule_Get`) are 124 guaranteed to succeed. 125 126 Return a nonzero value if the object is valid and matches the name passed in. 127 Return ``0`` otherwise. This function will not fail. 128 129 130.. c:function:: int PyCapsule_SetContext(PyObject *capsule, void *context) 131 132 Set the context pointer inside *capsule* to *context*. 133 134 Return ``0`` on success. Return nonzero and set an exception on failure. 135 136 137.. c:function:: int PyCapsule_SetDestructor(PyObject *capsule, PyCapsule_Destructor destructor) 138 139 Set the destructor inside *capsule* to *destructor*. 140 141 Return ``0`` on success. Return nonzero and set an exception on failure. 142 143 144.. c:function:: int PyCapsule_SetName(PyObject *capsule, const char *name) 145 146 Set the name inside *capsule* to *name*. If non-``NULL``, the name must 147 outlive the capsule. If the previous *name* stored in the capsule was not 148 ``NULL``, no attempt is made to free it. 149 150 Return ``0`` on success. Return nonzero and set an exception on failure. 151 152 153.. c:function:: int PyCapsule_SetPointer(PyObject *capsule, void *pointer) 154 155 Set the void pointer inside *capsule* to *pointer*. The pointer may not be 156 ``NULL``. 157 158 Return ``0`` on success. Return nonzero and set an exception on failure. 159