我正在尝试解压一个复杂的字典,但我在使用多个循环的列表理解表达式中得到了一个 NameError
:
a={
1: [{'n': 1}, {'n': 2}],
2: [{'n': 3}, {'n': 4}],
3: [{'n': 5}],
}
good = [1,2]
print [r['n'] for r in a[g] for g in good]
# NameError: name 'g' is not defined
最佳答案
你的循环顺序搞混了;它们被认为是从左到右嵌套的,因此 for r in a[g]
是 outer 循环并首先执行。交换循环:
print [r['n'] for g in good for r in a[g]]
现在 g
为下一个循环定义,for r in a[g]
,表达式不再引发异常:
>>> a={
... 1: [{'n': 1}, {'n': 2}],
... 2: [{'n': 3}, {'n': 4}],
... 3: [{'n': 5}],
... }
>>> good = [1,2]
>>> [r['n'] for g in good for r in a[g]]
[1, 2, 3, 4]
关于python - 名称未在具有多个循环的列表理解中定义,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/35479600/