def _output_msg(self, i, add=True):
    if add:
        txt1 = 'Adding'
        txt2 = 'to'
    else:
        txt1 = 'Removing'
        txt2 = 'from'
    print(f'{txt1} {self.output_fnames[i]} (unit={self.output_units[i]}) {txt2} the output list.')
def _output_msg(self, i, add=True):
    if add:
        txt1 = 'Adding'
        txt2 = 'to'
    else:
        txt1 = 'Removing'
        txt2 = 'from'
    print(f'{txt1} {self.output_fnames[i]} (unit={self.output_units[i]}) {txt2} the output list.')