method field is not called

Why the method field is not called when loading a dict?

from marshmallow import Schema, fields

class UserSchema(Schema):
    first_name = fields.Str(load_from='name')
    email = fields.Email()
    custom = fields.Method('yo')

    def yo(self, obj):
        return 'custom'

schema = UserSchema()
result = schema.load({'name': 'j', 'email': '[e-mail]'})
print result.data # prints {'first_name': u'j', 'email': u'[e-mail]'}   

[norbertpy]

Never mind. It’s only called when dumping not loading. But why?

[brettdh]

To elaborate: I needed to use the deserialize kwarg to Method() to get what I wanted, and the field had to be present to get processed.