File "electrum\gui\qt\main_window.py", line 3154, in on_exchange
  File "electrum\exchange_rate.py", line 565, in set_exchange
  File "electrum\simple_config.py", line 154, in set_key
  File "electrum\simple_config.py", line 163, in _set_key_in_user_config
  File "electrum\simple_config.py", line 243, in save_user_config