python如何实现多层级自动赋值字典

item['20161101'] = 2

item['20161101']["age"] = 2

import collections
bag = ['apple', 'orange', 'cherry', 'apple','apple', 'cherry', 'blueberry']
count = collections.defaultdict(int)
for fruit in bag:
    count[fruit] += 1
输出：
defaultdict(<class 'int'>, {'apple': 3, 'orange': 1, 'cherry': 2, 'blueberry': 1})

item['20161101']["age"]["444"] = 2

def __getitem__(self, item):
    try:
        return dict.__getitem__(self, item)
    except KeyError:
        value = self[item] = type(self)()
        return value

def __missing__(self, key):
    value = self[key] = type(self)()
    return value

class multidict(dict):
def __getitem__(self, item):
    try:
        return dict.__getitem__(self, item)
    except KeyError:
        value = self[item] = type(self)()
        return value
item = multidict()
item['20161101']["age"] = 20
item['20161102']['num'] = 30
print(item)

key = 0
value = [1,5]
exp = dict()
exp.setdefault(key,[]).append(value) 
value = [2,5]
exp.setdefault(key,[]).append(value)
print(exp)

key = 0
value = 1
exp = dict()
exp.setdefault(key,set()).add(value) 
value = 2
exp.setdefault(key,set()).add(value)
print(exp)

import collections
key = 0
value = 1
exp = collections.defaultdict(list)
exp[key].append(value)
value = 1
exp[key].append(value)
print(exp)

import collections
key = 0
value = 1
exp = collections.defaultdict(set)
exp[key].add(value)
value = 1
exp[key].add(value)
value = 5
exp[key].add(value)
print(exp)