Get values from dictionary by class as a key

Question

How can I make this work, I need to get values from dictionary by class as a key.

But I get TypeError: unhashable type: 'FirstClass'

from dataclasses import dataclass


@dataclass
class FirstClass():
    name: str


@dataclass
class SecondClass():
    name: str


MAPPER = {FirstClass: 888, SecondClass: 999}

itr_list = [FirstClass(name="default_name"), SecondClass(name="default_name")]

for itr in itr_list:
    get_key = MAPPER[itr]

Does this answer your question? [How can I make a python dataclass hashable without making them immutable?](https://stackoverflow.com/questions/52390576/how-can-i-make-a-python-dataclass-hashable-without-making-them-immutable) — 9769953, Jul 21 '22 at 11:33
Note that the suggested duplicate also has answers with a solution to do this for immutable dataclasses, which might also work for your case. — 9769953, Jul 21 '22 at 11:34
when access items in a dict you have to use the same key as you constructed it with. `FirstClass` (the class itself) is not the same as `FirstClass(name="default_name")` (an instance of that class) — Anentropic, Jul 21 '22 at 11:36
@9769953 I got perfect answer for my needs from Pranav Hosangadi, thank you — Chaban33, Jul 21 '22 at 11:37

score 3 · Accepted Answer · answered Jul 21 '22 at 11:34

Your problem is that you use the type FirstClass and SecondClass to define MAPPER, but you use an instance of those classes to lookup MAPPER[itr]. It will work if you use the type instead, like so: MAPPER[type(itr)].

for itr in itr_list:
    get_key = MAPPER[type(itr)]
    print(get_key)

will output

888
999

Get values from dictionary by class as a key

1 Answers1