Python列表索引错误

Question

这是我现在的版本的代码，我不断收到列表索引错误。

n = 0 
y = len(list1)-1 
while n < y: 
    for k in list1: 
     if list1[n]+ k == g: 
      print("The 2 prime numbers that add up to ",g,"are ", list1[n]," and ",k,".") 
      break 
     else: 
      n = n+1 

Answer 1

您在for循环递增n但在外部while循环测试其contraint。

也许这就是你想要的东西：

n = 0 
y = len(list1)-1 
found = 0 
while n < y: 
    for k in list1: 
     if list1[n]+ k == g: 
      print("The 2 prime numbers that add up to ",g,"are ", list1[n]," and ",k,".") 
      found = 1 
      break # for loop 
    if found: 
     break # while loop 
    n = n + 1 

一个更好的办法做到这一点是使用itertools.combinations_with_replacement：

import itertools 
for (v1,v2) in itertools.combinations_with_replacement(list1, 2): 
    if v1 + v2 == g: 
     print("blah blah blah") 
     break 

combinations_with_replacement(list1,2)将返回list1两种元素的所有无序组合。例如，combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC

Answer 2

您留下了一些信息，但我收集到您正在尝试查找与目标相匹配的2个素数。为了以这种方式访问​​列表，您需要枚举它。

y = len(list1) - 1 
while n < y: 
    for n, k in enumerate(list1): 
     if list1[n]+ k == g : 
      print("The 2 prime numbers that add up to ",g,"are ", list1[n]," and ",k,".") 
      break 

但是，你并不真的需要索引，两个for循环会完成同样的事情。

target = 8 
primes = [2, 3, 5, 7, 11, 13, 17, 19] 
message = 'The 2 prime numbers that add up to {target} are {value1} and {value2}' 
for index1, value1 in enumerate(primes): 
    for value2 in primes[index1 + 1:]: 
     if value1 + value2 == target: 
      print(message.format(target=target, value1=value1, value2=value2))