如何创建一个字典，其中键是来自另一个字典的值?

Question

给定下列对象列表a:

a = [
{"class": "math", "grade": 90},
{"class": "english", "grade": 80},
{"class": "science", "grade": 70},
]

如何创建一个字典，其中键是每个对象的"类"的值;列表中的成员"值是0吗?

从"a":

派生的所需数据结构

b = {
"math": 0,
"english": 0,
"science": 0
}

Answer 1

您可以像下面这样使用字典推导式:

a = [
{"class": "math", "grade": 90},
{"class": "english", "grade": 80},
{"class": "science", "grade": 70},
]
b = {x["class"]: 0 for x in a}

或,字典理解:

a = [
{"class": "math", "grade": 90},
{"class": "english", "grade": 80},
{"class": "science", "grade": 70},
]
b = {}
for obj in a:
b.setdefault(obj["class"], 0)