如何在 python 中使用列表理解来避免索引错误

Question

我有一个字典数组，我想检查特定的键是否在字典数组中并检索该项目。 我知道如何使用列表理解来做到这一点，但是有没有办法在不这样做的情况下避免索引错误？

result = [x[fruit]["weight"] for x in [{"apple":{"weight":0.25}},{"orange":{"weight":0.25}}] if fruit in x.keys()]
if result:
   weight_of_fruit = result[0]

我宁愿这样做：

result = [x[fruit]["weight"] for x in [{"apple":{"weight":0.25}},{"orange":{"weight":0.25}}] if fruit in x.keys()][0]

但这有indexError的风险。

我可以用类似于 dict .get() 方法的数组做一些事情吗？所以我可以用一行干净的代码来编写它。

Answer 1

我仍然认为它很难看且难以阅读，但如果你真的必须，请使用

fruit = 'unknown'
result = [x[fruit]["weight"] if fruit in x.keys() else None for x in [{"apple":{"weight":0.25}},{"orange":{"weight":0.25}}]][0]

请记住，我更改了

if fruit in x.keys()

的顺序并添加了

else None

Answer 2

您可以使用

next()

默认值：

lst = [{"apple": {"weight": 0.25}}, {"orange": {"weight": 0.25}}]

fruit = "pear"
result = next((d[fruit]["weight"] for d in lst if fruit in d), [])

print(result)

打印：

[]