首先，你需要列出所有的文件在目录与.midi扩展名。

import os
import music21 as m

# traverse whole directory
for root, dirs, files in os.walk(r'd:/somedir/'):
    # select the file name
    for file in files:
        # check if it is MIDI
        if file.endswith('.midi'):
            # get full path of the file
            midi_file = os.path.join(root, file)
            #score = m.converter.parse(midi_file)
            key = m.converter.parse(midi_file).analyze('key')
            print(file, key.tonic.name, key.mode)