File "/usr/local/lib/python3.5/dist-packages/electrum_gui/qt/main_window.py", line 2936, in on_fiat_address
    self.fx.set_fiat_address_config(checked)
  File "/usr/local/lib/python3.5/dist-packages/electrum/exchange_rate.py", line 484, in set_fiat_address_config
    self.config.set_key('fiat_address', bool(b))
  File "/usr/local/lib/python3.5/dist-packages/electrum/simple_config.py", line 143, in set_key
    self._set_key_in_user_config(key, value, save)
  File "/usr/local/lib/python3.5/dist-packages/electrum/simple_config.py", line 152, in _set_key_in_user_config
    self.save_user_config()
  File "/usr/local/lib/python3.5/dist-packages/electrum/simple_config.py", line 219, in save_user_config
    f.write(s)