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binary_search.py

 # 使用二分查找法，找出9和20在列表里面的索引
 b=20
 num_list = [1, 3, 5, 8, 11, 15, 17, 18, 20, 21]
-low=0
+def p(b)
+low=0 
 high=len(num_list)-1
 while high>low:
     mid=(low+high)//2