# 读取文件内容
def read_file(filename):
    try:
        with open(filename, 'r') as file:
            content = file.read()
        return content
    except FileNotFoundError:
        print(f"File '{filename}' not found.")
        return None

# 写入文件（覆盖原有内容）
def write_file(filename, content):
    try:
        with open(filename, 'w') as file:
            file.write(content)
    except PermissionError:
        print(f"No permission to write to file '{filename}'.")

# 追加内容到文件
def append_to_file(filename, content):
    try:
        with open(filename, 'a') as file:
            file.write(content)
    except PermissionError:
        print(f"No permission to append to file '{filename}'.")

content = read_file('input.txt')
write_file('output.txt', 'New content')
append_to_file('log.txt', '\nAdditional log entry')

import os

def list_files_recursively(directory, extension=None):
    for root, dirs, files in os.walk(directory):
        for file in files:
            if extension is None or file.endswith(extension):
                yield os.path.join(root, file)

for file_path in list_files_recursively('.', '.txt'):
    print(file_path)

import os
import pwd
import grp

def get_permissions(path):
    stats = os.stat(path)
    mode = stats.st_mode & 0o777
    return oct(mode)

def change_owner(path, user, group):
    uid = pwd.getpwnam(user).pw_uid
    gid = grp.getgrnam(group).gr_gid
    os.chown(path, uid, gid)

permissions = get_permissions('/path/to/file')
print(permissions)

change_owner('/path/to/directory', 'new_user', 'new_group')