Larry Hastings | 402b73f | 2010-03-25 00:54:54 +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 | |
| 37 | .. cfunction:: PyObject* PyCapsule_New(void *pointer, const char *name, PyCapsule_Destructor destructor) |
| 38 | |
| 39 | Create a :ctype:`PyCapsule` encapsulating the *pointer*. The *pointer* |
| 40 | argument may not be *NULL*. |
| 41 | |
| 42 | On failure, set an exception and return *NULL*. |
| 43 | |
| 44 | The *name* string may either be *NULL* or a pointer to a valid C string. If |
| 45 | non-*NULL*, this string must outlive the capsule. (Though it is permitted to |
| 46 | free it inside the *destructor*.) |
| 47 | |
| 48 | If the *destructor* argument is not *NULL*, it will be called with the |
| 49 | capsule as its argument when it is destroyed. |
| 50 | |
| 51 | If this capsule will be stored as an attribute of a module, the *name* should |
| 52 | be specified as ``modulename.attributename``. This will enable other modules |
| 53 | to import the capsule using :cfunc:`PyCapsule_Import`. |
| 54 | |
| 55 | |
| 56 | .. cfunction:: void* PyCapsule_GetPointer(PyObject *capsule, const char *name) |
| 57 | |
| 58 | Retrieve the *pointer* stored in the capsule. On failure, set an exception |
| 59 | and return *NULL*. |
| 60 | |
| 61 | The *name* parameter must compare exactly to the name stored in the capsule. |
| 62 | If the name stored in the capsule is *NULL*, the *name* passed in must also |
| 63 | be *NULL*. Python uses the C function :cfunc:`strcmp` to compare capsule |
| 64 | names. |
| 65 | |
| 66 | |
| 67 | .. cfunction:: PyCapsule_Destructor PyCapsule_GetDestructor(PyObject *capsule) |
| 68 | |
| 69 | Return the current destructor stored in the capsule. On failure, set an |
| 70 | exception and return *NULL*. |
| 71 | |
| 72 | It is legal for a capsule to have a *NULL* destructor. This makes a *NULL* |
| 73 | return code somewhat ambiguous; use :cfunc:`PyCapsule_IsValid` or |
| 74 | :cfunc:`PyErr_Occurred` to disambiguate. |
| 75 | |
| 76 | |
| 77 | .. cfunction:: void* PyCapsule_GetContext(PyObject *capsule) |
| 78 | |
| 79 | Return the current context stored in the capsule. On failure, set an |
| 80 | exception and return *NULL*. |
| 81 | |
| 82 | It is legal for a capsule to have a *NULL* context. This makes a *NULL* |
| 83 | return code somewhat ambiguous; use :cfunc:`PyCapsule_IsValid` or |
| 84 | :cfunc:`PyErr_Occurred` to disambiguate. |
| 85 | |
| 86 | |
| 87 | .. cfunction:: const char* PyCapsule_GetName(PyObject *capsule) |
| 88 | |
| 89 | Return the current name stored in the capsule. On failure, set an exception |
| 90 | and return *NULL*. |
| 91 | |
| 92 | It is legal for a capsule to have a *NULL* name. This makes a *NULL* return |
| 93 | code somewhat ambiguous; use :cfunc:`PyCapsule_IsValid` or |
| 94 | :cfunc:`PyErr_Occurred` to disambiguate. |
| 95 | |
| 96 | |
| 97 | .. cfunction:: void* PyCapsule_Import(const char *name, int no_block) |
| 98 | |
| 99 | Import a pointer to a C object from a capsule attribute in a module. The |
| 100 | *name* parameter should specify the full name to the attribute, as in |
| 101 | ``module.attribute``. The *name* stored in the capsule must match this |
| 102 | string exactly. If *no_block* is true, import the module without blocking |
| 103 | (using :cfunc:`PyImport_ImportModuleNoBlock`). If *no_block* is false, |
| 104 | import the module conventionally (using :cfunc:`PyImport_ImportModule`). |
| 105 | |
| 106 | Return the capsule's internal *pointer* on success. On failure, set an |
| 107 | exception and return *NULL*. However, if :cfunc:`PyCapsule_Import` failed to |
| 108 | import the module, and *no_block* was true, no exception is set. |
| 109 | |
| 110 | .. cfunction:: int PyCapsule_IsValid(PyObject *capsule, const char *name) |
| 111 | |
| 112 | Determines whether or not *capsule* is a valid capsule. A valid capsule is |
| 113 | non-*NULL*, passes :cfunc:`PyCapsule_CheckExact`, has a non-*NULL* pointer |
| 114 | stored in it, and its internal name matches the *name* parameter. (See |
| 115 | :cfunc:`PyCapsule_GetPointer` for information on how capsule names are |
| 116 | compared.) |
| 117 | |
| 118 | In other words, if :cfunc:`PyCapsule_IsValid` returns a true value, calls to |
| 119 | any of the accessors (any function starting with :cfunc:`PyCapsule_Get`) are |
| 120 | guaranteed to succeed. |
| 121 | |
| 122 | Return a nonzero value if the object is valid and matches the name passed in. |
| 123 | Return 0 otherwise. This function will not fail. |
| 124 | |
| 125 | .. cfunction:: int PyCapsule_SetContext(PyObject *capsule, void *context) |
| 126 | |
| 127 | Set the context pointer inside *capsule* to *context*. |
| 128 | |
| 129 | Return 0 on success. Return nonzero and set an exception on failure. |
| 130 | |
| 131 | .. cfunction:: int PyCapsule_SetDestructor(PyObject *capsule, PyCapsule_Destructor destructor) |
| 132 | |
| 133 | Set the destructor inside *capsule* to *destructor*. |
| 134 | |
| 135 | Return 0 on success. Return nonzero and set an exception on failure. |
| 136 | |
| 137 | .. cfunction:: int PyCapsule_SetName(PyObject *capsule, const char *name) |
| 138 | |
| 139 | Set the name inside *capsule* to *name*. If non-*NULL*, the name must |
| 140 | outlive the capsule. If the previous *name* stored in the capsule was not |
| 141 | *NULL*, no attempt is made to free it. |
| 142 | |
| 143 | Return 0 on success. Return nonzero and set an exception on failure. |
| 144 | |
| 145 | .. cfunction:: int PyCapsule_SetPointer(PyObject *capsule, void *pointer) |
| 146 | |
| 147 | Set the void pointer inside *capsule* to *pointer*. The pointer may not be |
| 148 | *NULL*. |
| 149 | |
| 150 | Return 0 on success. Return nonzero and set an exception on failure. |