CODEWITHSUNDEEP
python-3.xserializationpickletyping
Matti Lyra
Matti Lyra

Reputation: 13088

Python typing, pickle and serialisation

I've started learning the typing system in python and came across an issue in defining function arguments that are picklable. Not everything in python can be pickled, can I define a type annotation that says "only accept objects that can are picklable"?

At first it sounds like something that should be possible, similar to Java's Serializable but then there is no Picklable interface in python and thinking about the issue a little more it occurs to me that pickling is an inherently runtime task. What can be pickled lists a number of things that can be pickled, and it's not difficult to imagine a container of lambda functions which would not be picklable, but I can't think of a way of determining that before hand (without touching the container definition).

The only way I've come up with is to define something like a typing.Union[Callable, Iterable, ...] of all the things listed in What can be pickled but that does not seem like a good solution.

Upvotes: 4

Views: 2571

Answers (1)

Matti Lyra
Matti Lyra

Reputation: 13088

This issue on github partially answers the question, although the issue is specifically related to json not pickle but the first answer from Guido should still apply to pickle

I tried to do that but a recursive type alias doesn't work in mypy right now, and I'm not sure how to make it work. In the mean time I use JsonDict = Dict[str, Any] (which is not very useful but at least clarifies that the keys are strings), and Any for places where a more general JSON type is expected.

https://github.com/python/typing/issues/182

Upvotes: 2

Related Questions