contextvars_quickstart_create_set_get_reset_state.py

1from contextvars import ContextVar
2
3# Declare a context variable
4var: ContextVar[str] = ContextVar('var', default='default')
5
6def main():
7    # Get the value; returns 'default' as it hasn't been set yet
8    print(var.get())
9
10    # Set a new value and keep the token
11    token = var.set('new value')
12    try:
13        # Get the new value
14        print(var.get())  # 'new value'
15    finally:
16        # Reset the variable to the previous value
17        var.reset(token)
18
19    # After reset, it returns to 'default'
20    print(var.get())
21
22if __name__ == '__main__':
23    main()