Inconsistent error messages using a nested partial schema.

I have these schemas.

class MySchema(Schema):
    title = fields.String(required=True)


class Wrapped(Schema):
    wrapped = fields.Nested(MySchema(partial=True), required=True)

s = Wrapped()

print(s.load({}))
UnmarshalResult(data={}, errors={'wrapped': {'title': ['Missing data for required field.']}})

Since MySchema is a nested partial in Wrapped, required errors related to MySchema should not appear when I send in an empty dict as data. At least thats what I would except. Rather the error should only say that the required field wrapped is missing.

I understand this might be a weird example. But it does seem like a subtle bug. Removing required is also not what I want because I want to be able to assume that if the schema is valid, I at least have an output like: {'wrapped': {}}

Using marshmallow 2.11.1

[maximkulkin]

I ended up creating my own fork that fixes that problem. We use it in my company. Later on I even created my own library similar to Marshmallow and right now we are transitioning to this new library.

You can start with a fork and later put pressure on Marshmallow maintainers to remove that offending feature.

[maximkulkin]

I think it all roots in the same crazy idea to report all required fields for all nested objects regardless of what actual payload looks like. Consider this example: https://github.com/marshmallow-code/marshmallow/issues/319#issuecomment-232221049. I guess implementation for this feature takes precedence to partial.