Python列表索引錯誤

Question

這是我現在的版本的代碼，我不斷收到列表索引錯誤。

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循環遞增n但在外部while循環測試其contraint。

也許這就是你想要的東西：

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 

一個更好的辦法做到這一點是使用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)將返回list1兩種元素的所有無序組合。例如，combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC

Answer 2

您留下了一些信息，但我收集到您正在嘗試查找與目標相匹配的2個素數。爲了以這種方式訪問​​列表，您需要枚舉它。

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，你並不真的需要索引，兩個for循環會完成同樣的事情。

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))