Python 二分查找

def search(data_set,find_num):
    mid = len(data_set) /2
    print mid
    if len(data_set) == 1:
       if data_set[mid] == find_num:
        print ('End start: ',find_num)
        return
       else:
        print ('NO NO NO:',find_num)
        return
    if data_set[mid] == find_num:
        print ('find start:',find_num)
        return
    elif data_set[mid] > find_num:
        print ('in left',data_set[:mid])
        search(data_set[:mid],find_num)
    elif  data_set[mid] < find_num:
        print ('in right',data_set[mid:])
        search(data_set[mid:],find_num)

if __name__ == '__main__':
    data = range(1,20,3)
    print (data)
    find = input('num:')
    search(data,find)