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')