Make unit model hashable

[tstorek]

Is your feature request related to a problem? Please describe.
Currently, the units model is not hashable although the content should be immutable and, hence, frozen.
But due to the missing Config in the model the __hash__ function is not generated by pydantic.

Describe the solution you'd like
I would like to add the following content to the model:

class Unit(BaseModel):
    ...

    class Config:
        extra = 'ignore'
        allow_population_by_field_name = True
        allow_mutation = False
        frozen = True
           

Describe alternatives you've considered
Inherit, the Unit model and add a specific Config object. However, this may lead to inconssitency

Additional context
Use case:
I have a list ob sensors that also contains information about the unit.
For mapping measurements to the sepcific sensors I regularly must loop throuth this list. Therefore, caching such lookup can be wuite useful. Caching though requires hashing of the Objects in the list that I qant to operate on.

[djs0109]

Hello @tstorek , thanks for the detailed report, it makes sense to me. Can you describe a bit more what do you mean by "caching", and what kind of error you have received while trying to cach? It could be useful to other users, who later come into the same problem. But anyway, it is nice to hear from you! :)

[tstorek]

@djs0109 Python supports builtin caching of functions as long as all args are hashable. Using this minimized access time if the function call is identical with a former function call because the function reponse was already caluculated earlier. This is quite useful for filtering etc.