Python帮助：全局定义的项目不断产生未定义的错误

Question

PSA：Python 学习者（30 天，还在增加）。 我正在尝试创建一个 python 脚本，它创建一个视频播放列表，这些视频是从给定文件夹/子文件夹中随机选择的。当我运行它时，我在脚本的第 40 行（在“#create a VLC playlist in select folder”部分）出现“'selected_files' is not defined”错误，当我在全局范围内明确定义它时......我思考。欢迎协助。

import os
import random
    
def find_files(folder, extensions):
    files = []
    for root, dirs, filenames in os.walk(folder):
        for filename in filenames:
            if any(filename.endswith(ext) for ext in extensions):
                files.append(os.path.join(root, filename))
    return files

def main():
    global selected_files
    # specify the folders to search and the file extensions to search for
    folders = [r"path\to\show1", r"path\to\show2", r"path\to\show3", r"path\to\show4"]
        
    extensions = (".mp4", ".avi", ".mkv")

    selected_files = []
    for folder in folders:
        files = find_files(folder, extensions)
        if files:
            selected_files.append(random.choice(files))
        else:
            print(f"No files found in {folder}.")
    if not selected_files:
        print("No files found.")
        return
    
# create a VLC playlist in select folder
playlist_folder = r"path\where\playlist\is\saved"
if not os.path.exists(playlist_folder):
    os.makedirs(playlist_folder)
playlist_file = os.path.join(playlist_folder, "PMTV.xspf")
with open(playlist_file, "w", encoding='utf8') as f:
    f.write('<?xml version="1.0" encoding="UTF-8"?>\n')
    f.write('<playlist xmlns="http://xspf.org/ns/0/" xmlns:vlc="http://www.videolan.org/vlc/playlist/ns/0/" version="1">\n')
    f.write('\t<title></title>\n')
    f.write('\t<trackList>\n')
    for file in selected_files:
        f.write('\t\t<track>\n')
        f.write(f'\t\t\t<location>{file}</location>\n')
        f.write('\t\t\t<title></title>\n')
        f.write('\t\t\t<duration></duration>\n')
        f.write('\t\t\t<extension application="http://www.videolan.org/vlc/playlist/0">\n')
        f.write('\t\t\t\t<vlc:id></vlc:id>\n')
        f.write('\t\t\t</extension>\n')
        f.write('\t\t</track>\n')
    f.write('\t</trackList>\n')
    f.write('</playlist>\n')
print(f"{len(selected_files)} files added to {playlist_file}")
    
if __name__ == "__main__":
    main()

Answer 1

加载脚本时，代码位于

# create a VLC playlist in select folder

...在到达 main 之前被执行

它向你吐槽，因为 selected_files 尚未定义。 ...所以通过插入

selected_files=[]

你定义它，然后停止呕吐。

现在，除此之外，您在这方面可能存在逻辑错误，因为当您在 for file in selected_files: 进入循环时，selected_files 不包含任何内容 - 在第 40 行 - 因为它尚未填充项目。