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185 lines
6.0 KiB
ReStructuredText
185 lines
6.0 KiB
ReStructuredText
.. highlight:: c
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.. _contextvarsobjects:
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Context Variables Objects
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-------------------------
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.. _contextvarsobjects_pointertype_change:
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.. versionadded:: 3.7
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.. versionchanged:: 3.7.1
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.. note::
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In Python 3.7.1 the signatures of all context variables
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C APIs were **changed** to use :c:type:`PyObject` pointers instead
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of :c:type:`PyContext`, :c:type:`PyContextVar`, and
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:c:type:`PyContextToken`, e.g.::
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// in 3.7.0:
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PyContext *PyContext_New(void);
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// in 3.7.1+:
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PyObject *PyContext_New(void);
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See :issue:`34762` for more details.
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This section details the public C API for the :mod:`contextvars` module.
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.. c:type:: PyContext
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The C structure used to represent a :class:`contextvars.Context`
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object.
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.. c:type:: PyContextVar
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The C structure used to represent a :class:`contextvars.ContextVar`
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object.
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.. c:type:: PyContextToken
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The C structure used to represent a :class:`contextvars.Token` object.
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.. c:var:: PyTypeObject PyContext_Type
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The type object representing the *context* type.
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.. c:var:: PyTypeObject PyContextVar_Type
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The type object representing the *context variable* type.
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.. c:var:: PyTypeObject PyContextToken_Type
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The type object representing the *context variable token* type.
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Type-check macros:
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.. c:function:: int PyContext_CheckExact(PyObject *o)
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Return true if *o* is of type :c:data:`PyContext_Type`. *o* must not be
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``NULL``. This function always succeeds.
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.. c:function:: int PyContextVar_CheckExact(PyObject *o)
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Return true if *o* is of type :c:data:`PyContextVar_Type`. *o* must not be
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``NULL``. This function always succeeds.
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.. c:function:: int PyContextToken_CheckExact(PyObject *o)
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Return true if *o* is of type :c:data:`PyContextToken_Type`.
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*o* must not be ``NULL``. This function always succeeds.
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Context object management functions:
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.. c:function:: PyObject *PyContext_New(void)
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Create a new empty context object. Returns ``NULL`` if an error
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has occurred.
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.. c:function:: PyObject *PyContext_Copy(PyObject *ctx)
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Create a shallow copy of the passed *ctx* context object.
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Returns ``NULL`` if an error has occurred.
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.. c:function:: PyObject *PyContext_CopyCurrent(void)
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Create a shallow copy of the current thread context.
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Returns ``NULL`` if an error has occurred.
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.. c:function:: int PyContext_Enter(PyObject *ctx)
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Set *ctx* as the current context for the current thread.
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Returns ``0`` on success, and ``-1`` on error.
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.. c:function:: int PyContext_Exit(PyObject *ctx)
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Deactivate the *ctx* context and restore the previous context as the
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current context for the current thread. Returns ``0`` on success,
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and ``-1`` on error.
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.. c:function:: int PyContext_AddWatcher(PyContext_WatchCallback callback)
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Register *callback* as a context object watcher for the current interpreter.
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Return an ID which may be passed to :c:func:`PyContext_ClearWatcher`.
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In case of error (e.g. no more watcher IDs available),
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return ``-1`` and set an exception.
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.. versionadded:: 3.14
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.. c:function:: int PyContext_ClearWatcher(int watcher_id)
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Clear watcher identified by *watcher_id* previously returned from
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:c:func:`PyContext_AddWatcher` for the current interpreter.
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Return ``0`` on success, or ``-1`` and set an exception on error
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(e.g. if the given *watcher_id* was never registered.)
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.. versionadded:: 3.14
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.. c:type:: PyContextEvent
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Enumeration of possible context object watcher events:
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- ``Py_CONTEXT_EVENT_ENTER``
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- ``Py_CONTEXT_EVENT_EXIT``
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.. versionadded:: 3.14
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.. c:type:: int (*PyContext_WatchCallback)(PyContextEvent event, PyContext* ctx)
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Type of a context object watcher callback function.
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If *event* is ``Py_CONTEXT_EVENT_ENTER``, then the callback is invoked
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after *ctx* has been set as the current context for the current thread.
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Otherwise, the callback is invoked before the deactivation of *ctx* as the current context
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and the restoration of the previous contex object for the current thread.
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If the callback returns with an exception set, it must return ``-1``; this
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exception will be printed as an unraisable exception using
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:c:func:`PyErr_FormatUnraisable`. Otherwise it should return ``0``.
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There may already be a pending exception set on entry to the callback. In
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this case, the callback should return ``0`` with the same exception still
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set. This means the callback may not call any other API that can set an
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exception unless it saves and clears the exception state first, and restores
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it before returning.
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.. versionadded:: 3.14
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Context variable functions:
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.. c:function:: PyObject *PyContextVar_New(const char *name, PyObject *def)
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Create a new ``ContextVar`` object. The *name* parameter is used
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for introspection and debug purposes. The *def* parameter specifies
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a default value for the context variable, or ``NULL`` for no default.
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If an error has occurred, this function returns ``NULL``.
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.. c:function:: int PyContextVar_Get(PyObject *var, PyObject *default_value, PyObject **value)
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Get the value of a context variable. Returns ``-1`` if an error has
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occurred during lookup, and ``0`` if no error occurred, whether or not
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a value was found.
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If the context variable was found, *value* will be a pointer to it.
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If the context variable was *not* found, *value* will point to:
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- *default_value*, if not ``NULL``;
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- the default value of *var*, if not ``NULL``;
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- ``NULL``
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Except for ``NULL``, the function returns a new reference.
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.. c:function:: PyObject *PyContextVar_Set(PyObject *var, PyObject *value)
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Set the value of *var* to *value* in the current context. Returns
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a new token object for this change, or ``NULL`` if an error has occurred.
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.. c:function:: int PyContextVar_Reset(PyObject *var, PyObject *token)
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Reset the state of the *var* context variable to that it was in before
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:c:func:`PyContextVar_Set` that returned the *token* was called.
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This function returns ``0`` on success and ``-1`` on error.
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