# Context Variables Objects

Nuovo nella versione 3.7.

Cambiato nella versione 3.7.1:

Nota

In Python 3.7.1 the signatures of all context variables C APIs were changed to use `PyObject` pointers instead of `PyContext`, `PyContextVar`, and `PyContextToken`, e.g.:

    // in 3.7.0:
    PyContext *PyContext_New(void);

    // in 3.7.1+:
    PyObject *PyContext_New(void);

See bpo-34762 for more details.

This section details the public C API for the `contextvars` module.

type PyContext

  The C structure used to represent a `contextvars.Context` object.

type PyContextVar

  The C structure used to represent a `contextvars.ContextVar` object.

type PyContextToken

  The C structure used to represent a `contextvars.Token` object.

PyTypeObject PyContext_Type

  The type object representing the context type.

PyTypeObject PyContextVar_Type

  The type object representing the context variable type.

PyTypeObject PyContextToken_Type

  The type object representing the context variable token type.

Type-check macros:

int PyContext_CheckExact(PyObject *o)

  Return true if o is of type `PyContext_Type`. o must not be `NULL`. This function always succeeds.

int PyContextVar_CheckExact(PyObject *o)

  Return true if o is of type `PyContextVar_Type`. o must not be `NULL`. This function always succeeds.

int PyContextToken_CheckExact(PyObject *o)

  Return true if o is of type `PyContextToken_Type`. o must not be `NULL`. This function always succeeds.

Context object management functions:

PyObject *PyContext_New(void)
  Return value: New reference.

  Create a new empty context object. Returns `NULL` if an error has occurred.

PyObject *PyContext_Copy(PyObject *ctx)
  Return value: New reference.

  Create a shallow copy of the passed ctx context object. Returns `NULL` if an error has occurred.

PyObject *PyContext_CopyCurrent(void)
  Return value: New reference.

  Create a shallow copy of the current thread context. Returns `NULL` if an error has occurred.

int PyContext_Enter(PyObject *ctx)

  Set ctx as the current context for the current thread. Returns `0` on success, and `-1` on error.

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:

PyObject *PyContextVar_New(const char *name, PyObject *def)
  Return value: New reference.

  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`.

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.

PyObject *PyContextVar_Set(PyObject *var, PyObject *value)
  Return value: New reference.

  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.

int PyContextVar_Reset(PyObject *var, PyObject *token)

  Reset the state of the var context variable to that it was in before `PyContextVar_Set()` that returned the token was called. This function returns `0` on success and `-1` on error.