exit是交互式外壳的帮助器 –
sys.exit旨在用于程序。
The site module (which is imported automatically during startup, except if the -S command-line option is given) adds several constants to the built-in namespace (e.g. exit). They are useful for the interactive interpreter shell and should not be used in programs.
技术上，他们做的大多是相同的：提高SystemExit. sys.exit这样做在sysmodule.c：
static PyObject *
sys_exit(PyObject *self, PyObject *args)
{
PyObject *exit_code = 0;
if (!PyArg_UnpackTuple(args, “exit”, 0, 1, &exit_code))
return NULL;
/* Raise SystemExit so callers may catch it or clean up. */
PyErr_SetObject(PyExc_SystemExit, exit_code);
return NULL;
}
退出在site.py中定义：
class Quitter(object):
def __init__(self, name):
self.name = name
def __repr__(self):
return ‘Use %s() or %s to exit’ % (self.name, eof)
def __call__(self, code=None):
# Shells like IDLE catch the SystemExit, but listen when their
# stdin wrapper is closed.
try:
sys.stdin.close()
except:
pass
raise SystemExit(code)
__builtin__.quit = Quitter(‘quit’)
__builtin__.exit = Quitter(‘exit’)
注意，有一个第三个退出选项，即os._exit，退出时不调用清理处理程序，刷新stdio缓冲区等(并且通常只能在fork()之后的子进程中使用)。