Systemexit

SystemExit is a built-in exception in Python that signals the interpreter to terminate execution. It is a subclass of BaseException and is raised either explicitly by the programmer via raise SystemExit(code) or implicitly by the standard library function sys.exit([code]).

Code semantics: When SystemExit is raised, the interpreter unwinds the call stack, runs finally blocks, and then exits. If SystemExit is not caught by user code, the interpreter terminates with an exit status determined by the code attribute. If code is None, the exit status is 0. If code is an integer, that value is used as the exit status. If code is a string, the string is written to standard error and the exit status is 1. If code is another exception instance, its string representation is printed and the exit status is 1.

Catching: SystemExit can be caught with a try/except block, using except SystemExit as e. In that case, the code can be inspected via e.code, and the program may choose to suppress termination or re-raise the exception. Because SystemExit derives from BaseException rather than Exception, a bare except: clause will not catch it; thus catching SystemExit typically requires an explicit except SystemExit.

Relationship and usage: SystemExit is the conventional mechanism for terminating a Python program, distinct from signals or OS-level termination. It allows a program to signal a controlled exit and provides a payload that can be inspected by surrounding code if needed.

See also: sys.exit, KeyboardInterrupt, BaseException.