当python字典键的值是列表时显示所有值

Question

我被严重卡住了，不胜感激指向正确方向的手电筒。 我有一个要导入为文本文件的列表。 它有名称，每一行都有编号。 名称重复1、2或3次。 目标是使输出为{Key：[，，] ...}。 我只设法显示了其中一个值。

dictionary = {}
with open('%Filename%') as f:
    for line in f:
        num, key = line.strip().split()
        dictionary[key] = [num]
print(dictionary)

我希望输出为{'USA': ['15','91','99']...}相反，我得到的只是{'USA': ['99]...}

Answer 1

使用collection.defaultdict

例如：

from collections import defaultdict

dictionary = defaultdict(list)
with open('%Filename%') as f:
    for line in f:
        num, key = line.strip().split()
        dictionary[key].append(num)
print(dictionary)

---

或dict.setdefault

例如：

dictionary = {}
with open('%Filename%') as f:
    for line in f:
        num, key = line.strip().split()
        dictionary.setdefault(key, []).append(num)
print(dictionary)

• 注意：您需要使用list.append将元素追加到列表中。

Answer 2

dictionary = {}
with open('%Filename%') as f:
    for line in f:
        num, key = line.strip().split()
        if not key in dictionary:
            dictionary[key] = []
        dictionary[key].append(num)
print(dictionary)

Answer 3

使用dict.get很容易解决：

dictionary = {}
with open('%Filename%') as f:
    for line in f:
        num, key = line.strip().split()
        dictionary[key] = dictionary.get(key, []) + [num]
print(dictionary)