Context Variables Objects

Note

Changed in version 3.7.1:

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.

New in version 3.7.

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

PyContext

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

PyContextVar

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

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.

int PyContext_ClearFreeList()

Clear the context variable free list. Return the total number of freed items. This function always succeeds.

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.