defaultdict

[root@pc1 test1]# python3
Python 3.11.4 (main, Jul  5 2023, 14:15:25) [GCC 11.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from collections import defaultdict
>>> dict1 = defaultdict(int)
>>> dict2 = dict()
>>> dict1
defaultdict(<class 'int'>, {})
>>> dict2
{}
>>> dict1["aa"] += 5
>>> dict1
defaultdict(<class 'int'>, {'aa': 5})
>>> dict2["aa"] += 5
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
KeyError: 'aa'
>>> dict2
{}