如何停止python程序

import os, sys

import pandas as pd

import numpy as np

df=pd.DataFrame({'a':[1,2,3,4],

                'b':['a','b','c',np.nan],

                'c':['2017-09','2017-09-12','2017-08-22','2017-07-11'],

                'd':['2017-09','2017-12','2017-08','2017-07']})

t=df.iloc[2,:].tolist()

df.columns=t

print(df)

c=[1,2,5]

dic={1:2,2:3,3:4}

#print(dic.keys())

new_col=[]

for x in c:

    if x not in dic.keys():

        new_col.append(x)

if new_col:

    print(new_col)

    sys.exit(1)

print('ssss')