Script errors out with drives

[trenchcoatjedi]

root@Pi:~/system_sensors/src# python3 system_sensors.py settings.yaml
Traceback (most recent call last):
  File "/root/system_sensors/src/system_sensors.py", line 250, in <module>
    add_drives()
  File "/root/system_sensors/src/system_sensors.py", line 168, in add_drives
    drive_path = settings['sensors']['external_drives'][drive]
                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^
TypeError: string indices must be integers, not 'str'

This happens no matter what is entered for external drives in the settings.yaml