我和我的團(tuán)隊(duì)（Python 新手）編寫了以下代碼來生成與特定城市和相關(guān)術(shù)語相關(guān)的 Spotify 歌曲。如果用戶輸入的城市不在我們的 CITY_KEY_WORDS 列表中，那么它會(huì)告訴用戶輸入將添加到請(qǐng)求文件中，然后將輸入寫入文件。代碼如下：from random import shufflefrom typing import Any, Dict, Listimport spotipyfrom spotipy.oauth2 import SpotifyClientCredentialssp = spotipy.Spotify(    auth_manager=SpotifyClientCredentials(client_id="",                                          client_secret=""))CITY_KEY_WORDS = {    'london': ['big ben', 'fuse'],    'paris': ['eiffel tower', 'notre dame', 'louvre'],    'manhattan': ['new york', 'new york city', 'nyc', 'empire state', 'wall street', ],    'rome': ['colosseum', 'roma', 'spanish steps', 'pantheon', 'sistine chapel', 'vatican'],    'berlin': ['berghain', 'berlin wall'],}def main(city: str, num_songs: int) -> List[Dict[str, Any]]:    if city in CITY_KEY_WORDS:        """Searches Spotify for songs that are about `city`. Returns at most `num_songs` tracks."""        results = []        # Search for songs that have `city` in the title        results += sp.search(city, limit=50)['tracks']['items']  # 50 is the maximum Spotify's API allows        # Search for songs that have key words associated with `city`        if city.lower() in CITY_KEY_WORDS.keys():            for related_term in CITY_KEY_WORDS[city.lower()]:                results += sp.search(related_term, limit=50)['tracks']['items']        # Shuffle the results so that they are not ordered by key word and return at most `num_songs`        shuffle(results)        return results[: num_songs]該代碼對(duì)于“if”語句運(yùn)行良好（如果有人進(jìn)入我們列出的城市）。但是，當(dāng)運(yùn)行 else 語句時(shí)，在操作正常執(zhí)行后會(huì)出現(xiàn) 2 個(gè)錯(cuò)誤（它將用戶的輸入打印并寫入文件）。出現(xiàn)的錯(cuò)誤是：Traceback (most recent call last):  File "...", line 48, in <module>    display_tracks(tracks)  File "...", line 41, in display_tracks    for num, track in enumerate(tracks):TypeError: 'NoneType' object is not iterable請(qǐng)?jiān)徫胰狈χR(shí)，但請(qǐng)有人幫忙解決這個(gè)問題嗎？我們還想在最后創(chuàng)建一個(gè)歌曲的播放列表，但在這方面遇到了困難。