readlines()会自动关闭文件吗？open(fname).readlines()后需手动关闭吗？

Let me break this down clearly for you:

1. Does readlines() automatically close the file?
   No, the readlines() method itself does not close the file. It only reads all lines from the open file object into a list — the underlying file handle remains open after the method finishes running.

2. Do I need to manually close the file after running lines = open(fname).readlines()?
   Technically, Python's garbage collector might eventually close the file when the unreferenced file object is cleaned up (since file objects have a __del__ method that triggers a close). But this is not reliable:

   • Garbage collection timing varies across Python implementations (e.g., CPython vs. PyPy).
   • If the program exits before the GC runs, the file might not be properly flushed or closed, leading to data loss or resource leaks.
   • You also lose the ability to explicitly handle errors related to file operations.
     So yes, you should ensure the file is properly closed — but with that specific one-liner, you can't easily do it, because you didn't store a reference to the file object.

3. How to manually close the file if it's not auto-closed?
   The best approaches are:

   • Store the file object and call close() explicitly:

     file_handle = open(fname)
     lines = file_handle.readlines()
     file_handle.close()
     

     For extra safety, wrap this in a try/finally block to ensure close() runs even if an error occurs while reading.

   • Use a with statement (context manager) — this is the Pythonic way:

     with open(fname) as file_handle:
         lines = file_handle.readlines()
     

     The with block automatically closes the file when the code inside finishes, regardless of whether an exception is raised. This is the recommended method because it's safe, clean, and eliminates the need to remember manual closure.

内容的提问来源于stack exchange，提问作者FI-Info