skip_missing is gone, how to skip None elements ?

I saw that v2.0.0b removed the skip_missing option, claiming it skips the missing entries by default. However in my case (using mongoengine’s Document) a field is never missing: it returns None which is, strictly speaking, something…

I can see from the commit (https://github.com/marshmallow-code/marshmallow/commit/a3908d36967ac30764ceb66c52c99357425fbdec) that previous behavior of skipping empty values (like None or empty list/tuple) has been obliterated. Is there now a new way to do this ?

I’m thinking for now to overload the _serialize method of each field to check for the empty value and return the missing singleton in such a case… but this sound really cumbersome to me, there must be a better way !

[sloria]

Sorry for the delayed response on this.

How about using a post-dump method to remove any null values? Something like:

from marshmallow import Schema, fields, post_dump

class BaseSchema(Schema):
    SKIP_VALUES = set([None])

    @post_dump
    def remove_skip_values(self, data):
        return {
            key: value for key, value in data.items()
            if value not in self.SKIP_VALUES
        }


class MySchema(BaseSchema):
    foo = fields.Field()
    bar = fields.Field()


sch = MySchema()
sch.dump({'foo': 42, 'bar': None}).data  # {'foo': 42}

[Bachmann1234]

Howdy! Thanks @sloria for this. Though you will run into problems if you have dicts or anything not hashable. Luckily I just needed to filter Nones out so I could change it to

if value is not None