ImportError: no module named 'base64'

I need to use base64 to decode the downlink message, like the following code, but when I updating the py file to Fipy, it said ImportError: no module named ‘base64’.

import base64

if downlink_message:
print('decode result {} '.light.decode())
print(‘Received: {}, on port: {}’.format(downlink_message, port))
pump_running = True
print(“Stopping the pump”)
pump_running = False

How can I fix this problem. Thanks so much!