How to specify type hints for dictionary key and values of a dict?

Question

I have a dictionary like so:

d = { 'my_label': ClassInstance() }

I would like to specify type hints to indicate that keys are strings, and values are instances of ClassInstance.

Is this possible in Python 3.8?

I found TypedDict but that seems to attempt to indicate a fixed set of keys. I would to allow any string as key.

The code as shown will already infer ``d`` as desired. What else do you need? — MisterMiyagi, Mar 24 '21 at 14:10
While a tricky question, why would you (practically) want to specify type hints?. Another way could be to serialize your class instance into a JSON string and convert it back when you want. — coderman1234, Mar 24 '21 at 14:10
Does this answer your question? [Type hinting a collection of a specified type](https://stackoverflow.com/questions/24853923/type-hinting-a-collection-of-a-specified-type) — MisterMiyagi, Mar 24 '21 at 14:11
Well, I'm learning more about Python and don't know the answer to this question, so... may not be practical, but doesn't matter, right? I would appreciate if people down voting could give some info on what's wrong with it. — Edy Bourne, Mar 24 '21 at 14:26

score 7 · Accepted Answer · answered Mar 24 '21 at 14:12

Yes, it is possible in Python 3.8

First import dictionary type hint:

from typing import Dict

and add type hint as following:

d: Dict[str, ClassInstance] = { 'my_label': ClassInstance() }

In Python 3.9, it is possible to do this without importing Dict from typing (link to 3.9 documentation) as:

d: dict[str, ClassInstance] = { 'my_label': ClassInstance() }

score 2 · Answer 2 · answered Mar 24 '21 at 14:10

2

from typing import Dict

d: Dict[str, ClassInstance] = { 'my_label': ClassInstance() }

answered Mar 24 '21 at 14:10

AKX

2 Answers2