When to Use exit() vs. sys.exit() in Python?

Understanding the Distinction Between exit() and sys.exit() in Python

In the Python language, there exist two functions with similar names, exit() and sys.exit(). Both pertain to exiting a program, but there are key differences to consider when choosing between them.

sys.exit() vs. exit()

As stated in the documentation for exit(), it is a helper primarily intended for the interactive shell environment. When used in interactive mode, simply calling exit() will cause the interpreter to promptly exit. However, this function is not recommended for use in programs due to the cautions mentioned in the Python documentation.

When to Use sys.exit()

For programs, sys.exit() is the preferred choice. It raises a SystemExit exception, allowing code to catch and potentially clean up resources before the program terminates. Calling sys.exit() with an optional argument will set the exit status code for the program.

Technical Implementation Differences

Technically, both exit() and sys.exit() ultimately raise a SystemExit exception. However, they differ in their implementation. sys.exit() raises SystemExit directly in the sysmodule.c C module, while exit() is defined in site.py and _sitebuiltins.py and makes use of a Quitter class to raise the exception.

Other Exit Options

It's worth noting that there is a third option for exiting a Python program: os._exit. Unlike sys.exit(), os._exit bypasses cleanup handlers and flushes stdio buffers, making it suitable for use when cleanup routines are not desired. However, it should generally only be employed in child processes after a fork().

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