'Change a config option.
This function is called if sig_option_changed is received. If the
option changed is the dataframe format, then the leading \'%\' character
is stripped (because it can\'t be stored in the user config). Then,
the signal is emitted again, so that the new value is saved in the
user config.'

@Slot(str, object)
def change_option(self, option_name, new_value):

    if (option_name == 'dataframe_format'):
        assert new_value.startswith('%')
        new_value = new_value[1:]
    self.sig_option_changed.emit(option_name, new_value)
