Allow setting a global unknown setting

The new RAISE unknown setting can make the migration pretty painful, especially for those who are just fine with EXCLUDEing unknown keys. What about making this global default a configuration setting?

Something as simple as:

import marshmallow

marshmallow.DEFAULT_UNKNOWN_BEHAVIOR = marshmallow.EXCLUDE

I know it’s possible to subclass Schema, but that seems more heavy-handed.

[deckar01]

You can modify the base schema’s Meta class directly and your subclasses will inherit it.

from marshmallow import Schema, fields, EXCLUDE

Schema.Meta.unknown = EXCLUDE

class Test(Schema):
    foo = fields.Str()

Test().load({'foo': 'test', 'junk': 2})
# {'foo': 'test'}

[lafrech]

It should work. Could you please provide a repro case?