ag.py

import time
import threading


def generator():
    try:
        print('STARTED')
        time.sleep(5)
        yield 1
    finally:
        print('FINALIZED')


def close_it():
    print('Atttempting to close')
    try:
        gen.close()
    except BaseException as ex:
        print(f"Couldn't close {type(ex).__name__}: {ex}")
    else:
        print('Closed!')


gen = generator()

threading.Timer(1, close_it).start()
gen.send(None)

Output:

STARTED
Atttempting to close
Couldn't close ValueError: generator already executing
FINALIZED