使用os.walk遍历文件夹返回None值，触发TypeError问题求助

问题代码 #

import os

def find_folders(folders):
    for folder in folders:
       return folder

def find_directories(search_path,folder):
    for root, dirs, files in os.walk(search_path):
        for dir in dirs:
            if dir == folder:
                open_dir = os.path.join(root,dir)
                return open_dir
def find_abundance_files(directory):
    for root,dirs,files in os.walk(directory):
        for file in files:
            if file.endswith(".tsv"):
                return file
def main():
    search_path = r"/mnt/e/Thesis/Parasponia_RNAseq/kal_out/"
    folders=["Medtru_BUD","Medtru_FLOWER","Medtru_LEAF","Medtru_NODULE","Medtru_ROOT","Medtru_SEED"]
    folder = find_folders(folders)
    directory = find_directories(search_path,folder)
    abundance_file = find_abundance_files(directory)

if __name__=="__main__":
    main()

报错信息 #

Traceback (most recent call last):
  File "C:\Users\gidio\PycharmProjects\flask_blog\CalculateRPK_paired_end.py", line 105, in <module>
    main()
  File "C:\Users\gidio\PycharmProjects\flask_blog\CalculateRPK_paired_end.py", line 100, in main
    abundance_file = find_abundance_files(directory)
  File "C:\Users\gidio\PycharmProjects\flask_blog\CalculateRPK_paired_end.py", line 81, in find_abundance_files
    for root,dirs,files in os.walk(directory):
  File "C:\ProgramData\Anaconda3\lib\os.py", line 342, in walk
    return _walk(fspath(top), topdown, onerror, followlinks)
TypeError: expected str, bytes or os.PathLike object, not NoneType

错误原因 #

• find_folders函数逻辑失效：遍历文件夹列表时第一次循环就直接return folder，只会返回列表第一个元素Medtru_BUD，剩下的5个文件夹完全没处理；如果后续找不到这个文件夹，整个流程直接断档。
• find_directories无匹配时返回None：如果search_path里不存在指定的folder，函数遍历完所有目录也找不到匹配项，此时函数没有任何返回语句，默认返回None，这就是directory变量变成None的直接原因。
• 路径实际不存在：报错显示运行环境是Windows（路径含C:\Users），但代码里用的是Linux格式路径/mnt/e/...，如果这个路径在Windows下未正确挂载或拼写错误，os.walk遍历不到目标文件夹，find_directories自然返回None。
• find_abundance_files未做参数校验：当传入的directory是None时，直接调用os.walk(directory)就会触发TypeError，因为os.walk要求传入有效的路径字符串，不能是None。

内容的提问来源于stack exchange，提问作者gforg34