无法使用python读取文件

我正在尝试使用 python 3.8.5 读取文件的内容，但输出为空，我不明白我做错了什么。

这是代码：

import subprocess
import os

filename = "ls.out"
ls_command = "ls -la"
file = open(filename, "w")
subprocess.Popen(ls_command, stdout=file, shell=True)
file.close()

# So far, all is ok. The file "ls.out" is correctly created and filled with the output of "ls -la" command"

file = open(filename, "r")
for line in file:
    print(line)
file.close()

这个脚本的输出是空的，它不打印任何东西。看不到内容ls.out。

这里有什么不正确的？

回答

import subprocess
import os

filename = "ls.out"
ls_command = "ls -la"
file = open(filename, "w")
proc = subprocess.Popen(ls_command, stdout=file, shell=True)
proc.wait()
file.close()


file = open(filename, "r")
for line in file:
    print(line)
file.close()