Benjamin Peterson | b173f78 | 2009-05-05 22:31:58 +0000 | [diff] [blame^] | 1 | .. highlightlang:: c |
| 2 | |
| 3 | .. _capsules: |
| 4 | |
| 5 | Capsules |
| 6 | -------- |
| 7 | |
| 8 | .. index:: object: Capsule |
| 9 | |
| 10 | Refer to :ref:`using-capsules` for more information on using these objects. |
| 11 | |
| 12 | |
| 13 | .. ctype:: PyCapsule |
| 14 | |
| 15 | This subtype of :ctype:`PyObject` represents an opaque value, useful for C |
| 16 | extension modules who need to pass an opaque value (as a :ctype:`void\*` |
| 17 | pointer) through Python code to other C code. It is often used to make a C |
| 18 | function pointer defined in one module available to other modules, so the |
| 19 | regular import mechanism can be used to access C APIs defined in dynamically |
| 20 | loaded modules. |
| 21 | |
| 22 | .. ctype:: PyCapsule_Destructor |
| 23 | |
| 24 | The type of a destructor callback for a capsule. Defined as:: |
| 25 | |
| 26 | typedef void (*PyCapsule_Destructor)(PyObject *); |
| 27 | |
| 28 | See :cfunc:`PyCapsule_New` for the semantics of PyCapsule_Destructor |
| 29 | callbacks. |
| 30 | |
| 31 | |
| 32 | .. cfunction:: int PyCapsule_CheckExact(PyObject *p) |
| 33 | |
| 34 | Return true if its argument is a :ctype:`PyCapsule`. |
| 35 | |
| 36 | .. cfunction:: PyObject* PyCapsule_New(void* pointer, const char* name, PyCapsule_Destructor destructor) |
| 37 | |
| 38 | Create a :ctype:`PyCapsule` encapsulating the *pointer*. The *pointer* |
| 39 | argument may not be *NULL*. |
| 40 | |
| 41 | The *name* string may either be *NULL* or a pointer to a valid |
| 42 | C string. If non-*NULL*, this string must outlive the capsule. |
| 43 | (Though it is permitted to free it inside the *destructor*.) |
| 44 | |
| 45 | If the *destructor* argument is not *NULL*, |
| 46 | it will be called with the capsule ``PyObject *`` when it is destroyed. |
| 47 | |
| 48 | If this capsule will be stored as an attribute of a module, it |
| 49 | is strongly suggested that the *name* string be specified as:: |
| 50 | |
| 51 | modulename.attributename |
| 52 | |
| 53 | This will enable other modules to import the capsule |
| 54 | using :cfunc:`PyCapsule_Import`. |
| 55 | |
| 56 | Return a valid capsule on success. |
| 57 | On failure, set an exception and return *NULL*. |
| 58 | |
| 59 | |
| 60 | .. cfunction:: void* PyCapsule_GetPointer(PyObject* capsule, const char* name) |
| 61 | |
| 62 | Retrieve the *pointer* stored in the capsule. |
| 63 | |
| 64 | The *name* parameter must compare exactly to the name stored in the capsule. |
| 65 | If the name stored in the capsule is *NULL*, the *name* passed in must |
| 66 | also be *NULL*. If the name stored in the capsule is non-*NULL*, |
| 67 | the *name* passed in must also be non-*NULL*, and must match the name |
| 68 | stored in the capsule. Python uses the C function *strcmp* to compare |
| 69 | capsule names. |
| 70 | |
| 71 | Return the internal *pointer* on success. |
| 72 | On failure, set an exception and return *NULL*. |
| 73 | |
| 74 | |
| 75 | .. cfunction:: PyCapsule_Destructor PyCapsule_GetDestructor(PyObject* capsule) |
| 76 | |
| 77 | Return the current *destructor* stored in the capsule. |
| 78 | On failure, set an exception and return *NULL*. |
| 79 | |
| 80 | It is legal for a capsule to have a *NULL* destructor. |
| 81 | This makes a *NULL* return code somewhat ambiguous; |
| 82 | use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate. |
| 83 | |
| 84 | |
| 85 | .. cfunction:: void* PyCapsule_GetContext(PyObject* capsule) |
| 86 | |
| 87 | Return the current *context* stored in the capsule. |
| 88 | On failure, set an exception and return *NULL*. |
| 89 | |
| 90 | It is legal for a capsule to have a *NULL* context. |
| 91 | This makes a *NULL* return code somewhat ambiguous; |
| 92 | use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate. |
| 93 | |
| 94 | |
| 95 | .. cfunction:: const char* PyCapsule_GetName(PyObject* capsule) |
| 96 | |
| 97 | Return the current *name* stored in the capsule. |
| 98 | On failure, set an exception and return *NULL*. |
| 99 | |
| 100 | It is legal for a capsule to have a *NULL* name. |
| 101 | This makes a *NULL* return code somewhat ambiguous; |
| 102 | use :cfunc:`PyCapsule_IsValid` or :cfunc:`PyErr_Occurred` to disambugate. |
| 103 | |
| 104 | |
| 105 | .. cfunction:: void* PyCapsule_Import(const char* name, int no_block) |
| 106 | |
| 107 | Import a pointer to a C object from a ``capsule`` attribute in a module. |
| 108 | The *name* parameter should specify the full name to the attribute, as |
| 109 | in *"module.attribute"*. |
| 110 | The *name* stored in the capsule must match this string exactly. |
| 111 | If *no_block* is true, import the module without blocking |
| 112 | (using :cfunc:`PyImport_ImportModuleNoBlock`). |
| 113 | If *no_block* is false, import the module conventionally |
| 114 | (using :cfunc:`PyImport_ImportModule`). |
| 115 | |
| 116 | Return the capsule's internal *pointer* on success. |
| 117 | On failure, set an exception and return *NULL*. |
| 118 | Exception: if *PyCapsule_Import* failed to import the module, |
| 119 | and *no_block* was true, no exception is set. |
| 120 | |
| 121 | .. cfunction:: int PyCapsule_IsValid(PyObject* capsule, const char* name) |
| 122 | |
| 123 | Determines whether or not a :ctype:`PyObject \*` is a valid capsule. |
| 124 | A valid capsule is non-*NULL*, passes :cfunc:`PyCapsule_CheckExact`, |
| 125 | has a non-NULL *pointer*, and its internal name matches the |
| 126 | *name* parameter. (See :cfunc:`PyCapsule_GetPointer` for |
| 127 | information on how capsule names are compared.) |
| 128 | |
| 129 | In other words, if :cfunc:`PyCapsule_IsValid` returns a true value, |
| 130 | calls to any of the accessors (any function starting |
| 131 | with :cfunc:`PyCapsule_Get`) are guaranteed to succeed. |
| 132 | |
| 133 | Return a nonzero value if the object is valid and matches the name |
| 134 | passed in. |
| 135 | Return 0 otherwise. |
| 136 | This function will not fail. |
| 137 | |
| 138 | .. cfunction:: int PyCapsule_SetContext(PyObject* capsule, void* context) |
| 139 | |
| 140 | Set the context pointer inside *capsule* to *context*. |
| 141 | |
| 142 | Return 0 on success. |
| 143 | Return nonzero and set an exception on failure. |
| 144 | |
| 145 | .. cfunction:: int PyCapsule_SetDestructor(PyObject* capsule, void (*)(PyObject *) destructor) |
| 146 | |
| 147 | Set the destructor inside *capsule* to *destructor*. |
| 148 | |
| 149 | Return 0 on success. |
| 150 | Return nonzero and set an exception on failure. |
| 151 | |
| 152 | .. cfunction:: int PyCapsule_SetName(PyObject* capsule, const char* name) |
| 153 | |
| 154 | Set the name inside *capsule* to *name*. If non-*NULL*, the name |
| 155 | must outlive the capsule. If the previous *name* stored in the |
| 156 | capsule was not *NULL*, no attempt is made to free it. |
| 157 | |
| 158 | Return 0 on success. |
| 159 | Return nonzero and set an exception on failure. |
| 160 | |
| 161 | .. cfunction:: int PyCapsule_SetPointer(PyObject* capsule, void* pointer) |
| 162 | |
| 163 | Set the void pointer inside *capsule* to *pointer*. The pointer |
| 164 | may not be *NULL*. |
| 165 | |
| 166 | Return 0 on success. |
| 167 | Return nonzero and set an exception on failure. |
| 168 | |