.. highlight:: c
.. _contextvarsobjects:
Context Variables Objects
-------------------------
.. _contextvarsobjects_pointertype_change:
.. versionadded:: 3.7
.. versionchanged:: 3.7.1
.. note::
In Python 3.7.1 the signatures of all context variables
C APIs were **changed** to use :c:type:`PyObject` pointers instead
of :c:type:`PyContext`, :c:type:`PyContextVar`, and
:c:type:`PyContextToken`, e.g.::
// in 3.7.0:
PyContext *PyContext_New(void);
// in 3.7.1+:
PyObject *PyContext_New(void);
See :issue:`34762` for more details.
This section details the public C API for the :mod:`contextvars` module.
.. c:type:: PyContext
The C structure used to represent a :class:`contextvars.Context`
object.
.. c:type:: PyContextVar
The C structure used to represent a :class:`contextvars.ContextVar`
object.
.. c:type:: PyContextToken
The C structure used to represent a :class:`contextvars.Token` object.
.. c:var:: PyTypeObject PyContext_Type
The type object representing the *context* type.
.. c:var:: PyTypeObject PyContextVar_Type
The type object representing the *context variable* type.
.. c:var:: PyTypeObject PyContextToken_Type
The type object representing the *context variable token* type.
Type-check macros:
.. c:function:: int PyContext_CheckExact(PyObject *o)
Return true if *o* is of type :c:data:`PyContext_Type`. *o* must not be
``NULL``. This function always succeeds.
.. c:function:: int PyContextVar_CheckExact(PyObject *o)
Return true if *o* is of type :c:data:`PyContextVar_Type`. *o* must not be
``NULL``. This function always succeeds.
.. c:function:: int PyContextToken_CheckExact(PyObject *o)
Return true if *o* is of type :c:data:`PyContextToken_Type`.
*o* must not be ``NULL``. This function always succeeds.
Context object management functions:
.. c:function:: PyObject *PyContext_New(void)
Create a new empty context object. Returns ``NULL`` if an error
has occurred.
.. c:function:: PyObject *PyContext_Copy(PyObject *ctx)
Create a shallow copy of the passed *ctx* context object.
Returns ``NULL`` if an error has occurred.
.. c:function:: PyObject *PyContext_CopyCurrent(void)
Create a shallow copy of the current thread context.
Returns ``NULL`` if an error has occurred.
.. c:function:: int PyContext_Enter(PyObject *ctx)
Set *ctx* as the current context for the current thread.
Returns ``0`` on success, and ``-1`` on error.
.. c:function:: int PyContext_Exit(PyObject *ctx)
Deactivate the *ctx* context and restore the previous context as the
current context for the current thread. Returns ``0`` on success,
and ``-1`` on error.
Context variable functions:
.. c:function:: PyObject *PyContextVar_New(const char *name, PyObject *def)
Create a new ``ContextVar`` object. The *name* parameter is used
for introspection and debug purposes. The *def* parameter specifies
a default value for the context variable, or ``NULL`` for no default.
If an error has occurred, this function returns ``NULL``.
.. c:function:: int PyContextVar_Get(PyObject *var, PyObject *default_value, PyObject **value)
Get the value of a context variable. Returns ``-1`` if an error has
occurred during lookup, and ``0`` if no error occurred, whether or not
a value was found.
If the context variable was found, *value* will be a pointer to it.
If the context variable was *not* found, *value* will point to:
- *default_value*, if not ``NULL``;
- the default value of *var*, if not ``NULL``;
- ``NULL``
Except for ``NULL``, the function returns a new reference.
.. c:function:: PyObject *PyContextVar_Set(PyObject *var, PyObject *value)
Set the value of *var* to *value* in the current context. Returns
a new token object for this change, or ``NULL`` if an error has occurred.
.. c:function:: int PyContextVar_Reset(PyObject *var, PyObject *token)
Reset the state of the *var* context variable to that it was in before
:c:func:`PyContextVar_Set` that returned the *token* was called.
This function returns ``0`` on success and ``-1`` on error.
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