停止execfile调用的脚本执行

Question

有没有办法在用execfile函数调用的Python脚本中中断执行，而不使用if/else语句？我试过用exit()，但这样会导致main.py无法完成。

# main.py
print "Main starting"
execfile("script.py")
print "This should print"

# script.py
print "Script starting"
a = False

if a == False:
    # Sanity checks. Script should break here
    # <insert magic command>    

# I'd prefer not to put an "else" here and have to indent the rest of the code
print "this should not print"
# lots of lines below

Answer 1

普通的异常处理有什么问题呢？

scriptexit.py

class ScriptExit( Exception ): pass

main.py

from scriptexit import ScriptExit
print "Main Starting"
try:
    execfile( "script.py" )
except ScriptExit:
    pass
print "This should print"

script.py

from scriptexit import ScriptExit
print "Script starting"
a = False

if a == False:
    # Sanity checks. Script should break here
    raise ScriptExit( "A Good Reason" )

# I'd prefer not to put an "else" here and have to indent the rest of the code
print "this should not print"
# lots of lines below

Answer 2

# script.py
def main():
    print "Script starting"
    a = False

    if a == False:
        # Sanity checks. Script should break here
        # <insert magic command>    
        return;
        # I'd prefer not to put an "else" here and have to indent the rest of the code
    print "this should not print"
    # lots of lines bellow

if __name__ ==  "__main__":
    main();

我觉得Python这个部分（比如 __name__ == "__main__ 之类的）挺让人烦的。

Answer 3

main 可以把 execfile 放在一个 try/except 块里：sys.exit 会引发一个 SystemExit 异常，main 可以在 except 里捕捉到这个异常，这样如果需要的话，它就可以继续正常执行。也就是说，在 main.py 中：

try:
  execfile('whatever.py')
except SystemExit:
  print "sys.exit was called but I'm proceeding anyway (so there!-)."
print "so I'll print this, etc, etc"

而 whatever.py 可以使用 sys.exit(0) 或其他方式来结束 它自己的 执行。只要在调用 execfile 的地方和被 execfile 的地方达成一致，任何其他异常也可以使用——不过 SystemExit 特别合适，因为它的意思非常明确！