TypeError: Ellipsis is not a dataclass and cannot be turned into one.

[heckad]

from dataclasses import field
from decimal import Decimal
from typing import Tuple

from marshmallow_dataclass import dataclass


@dataclass(frozen=True)
class Signal:
    fields: Tuple[Decimal, ...] = field(default_factory=list)

This ellipsis means that all values in fields have Decimal type.

[lovasoa]

Unfortunately, marshmallow does not seem to support variable length Tuple. As per the documentation:

class marshmallow.fields.Tuple: A tuple field, composed of a fixed number of other Field classes or instances

@sloria : Any opinion ?

[heckad]

How to make frozen dataclass with a list?

[lovasoa]

How to make frozen dataclass with a list?

I think your best bet for now is to create your own VariableLengthTuple field. See marshmallow's documentation on custom fields.

Then, you can have:

@dataclass(frozen=True)
class Signal:
    fields: Tuple[Decimal, ...] = field(
        default_factory=tuple,
        metadata = {"marshmallow_field":VariableLengthTuple()})

[sloria]

desert (a fork of marshmallow_dataclass) added support for variadic tuples. The PR would be worth evalutating: https://github.com/python-desert/desert/pull/17

[lovasoa]

@sloria : Would you consider adding VariadicTuple to marshmallow itself?

[mikeholler]

We just ran into this as well. Support for variadic tuples would be cool but in the end the workaround is pretty simple (just using List now).

[deansg]

I'm not sure when/how, but it seems to me like this is now resolved (I tried with version 8.5.10). Can anyone else confirm?

[dairiki]

I'm not sure when/how, but it seems to me like this is now resolved (I tried with version 8.5.10). Can anyone else confirm?

This was indeed fixed in #221, which is included as of release 8.5.10. (I was working on fixing #181 and independently noticed and fixed this issue as well, unaware of this ticket.)