Python程序中为何不应使用exit()函数？

Great question! Let's break down why sys.exit() is the recommended way to exit a Python program, and why exit() is best left strictly to interactive shells:

• exit() isn't a core built-in function—it's injected by the site module
  The exit() function doesn't come with Python's foundational built-ins. It gets added to your global namespace by the site module, which loads automatically when you start Python unless you use the -S command-line flag (a common choice to speed up startup by skipping site-specific setup). If your program runs with -S, calling exit() will throw a NameError because the function simply doesn't exist in that context. sys.exit() on the other hand lives in the standard sys module—just import sys and it's reliably available across all Python execution environments.

• exit() is explicitly designed for interactive use only
  Python's official docs spell this out clearly: exit() exists solely to help users exit the interactive shell cleanly. Under the hood, it's actually an instance of site._Helper—if you type exit (without parentheses) in the shell, it even prints a friendly reminder: Use exit() or Ctrl-D (i.e. EOF) to exit. While it technically triggers a SystemExit exception (just like sys.exit()), using it in a script goes against its intended purpose.

• It creates unnecessary, fragile dependencies
  Relying on exit() ties your program to the site module being loaded. The site module handles non-essential tasks like setting up site-packages paths and adding interactive helpers—your script doesn't need any of that to run properly. Ditching this dependency makes your code more robust and portable, especially in constrained environments where site might be disabled.

• Clarity and adherence to best practices
  Using sys.exit() makes your code's intent crystal clear—any Python developer reading it will immediately understand you're intentionally exiting the program. exit() can confuse newer developers who might assume it's a core built-in, and it breaks consistency with the standard practices outlined in Python's documentation.

Python官方文档指出，exit()仅应在交互式shell中用于退出。site模块（启动时会自动导入，除非使用-S命令行选项）会向内置命名空间添加若干常量，这些常量仅适用于交互式解释器shell，不应在程序中使用。

内容的提问来源于stack exchange，提问作者Stevoisiak