RFC: Return deserialized data when strict=True

Status quo

load currently returns a namedtuple (UnmarshalResult) containing both the deserialized data and error messages.

from marshmallow import Schema, fields, ValidationError

class UserSchema(Schema):
    id = fields.Int(required=True)

    class Meta:
        strict = True


schema = UserSchema()
try:
    result = schema.load({'id': 42})
except ValidationError as e:
    print(e.messages)
assert result.data['id'] == 42

Proposed API

When strict=True, return only the deserialized data. Messages can already be accessed from ValidationError.messages.

from marshmallow import Schema, fields, ValidationError

class UserSchema(Schema):
    id = fields.Int(required=True)

    class Meta:
        strict = True


schema = UserSchema()
try:
    data = schema.load({'id': 42})
except ValidationError as e:
    print(e.messages)
assert data['id'] == 42

[maximkulkin]

@douglas-treadwell I vote not to do that. Once Marshmallow goes this route, there are plenty of option combinations to introduce as a new methods: loaddata(), loadmany(), loadstrictmany()…

@sloria I would rather opt to deprecate strict option at all and just do validation error exceptions all the time. Then load() could return just data in an nonconfusing way

[douglas-treadwell]

I am in favor of strict=True by default, but I think the API for load() returning different KINDS of data depending on configuration might be confusing.