Write a Python script that lists all files under a given directory path.

You can use the built‑in os module to walk through a directory tree. The following script accepts a path argument and prints every file it finds:

import os
import sys

def list_files(root):
    for dirpath, dirnames, filenames in os.walk(root):
        for f in filenames:
            print(os.path.join(dirpath, f))

if __name__ == "__main__":
    if len(sys.argv) != 2:
        print("Usage: python list_files.py <directory>")
        sys.exit(1)
    list_files(sys.argv[1])

os.walk yields a 3‑tuple for each directory: the path, a list of subdirectories, and a list of files. The script concatenates the directory path with each filename to produce an absolute path. Complexity is O(n) where n is the total number of files and directories visited. The script handles nested directories and ignores symbolic links by default. For large trees, you might want to add error handling for permission issues or use pathlib for a more modern approach.