python字典问题

Answer 1

>>> d = {}
>>> help(d.fromkeys)
Help on built-in function fromkeys:

fromkeys(...)
    dict.fromkeys(S[,v]) -> New dict with keys from S and values equal to v.
    v defaults to None.

The values ​​of all 5 elements are v, and as v is a complex type, it is passed by reference instead of value.

Answer 2

References, they all point to the same []. . .

Answer 3

Because those lists are the same.

Answer 4

Because [] 只会被初始化一次，然后所有的key都会引用到它，也就是浅拷贝, it can be implemented in another way:
First way:
in python3

d = {i: [] for i in range(5)}
d[1].append({'k': 'v'})

The second type:

from collections import defaultdict
d = defaultdict(list)
d[1].append({'k': 'v'})

copy.deepcopyI don’t really want to use it anymore