Nested class can't process dict about marshmallow

[sloria]

Aha, this is tricky case. marshmallow serializes objects by pulling attributes or keys from objects that correspond to the names of a serializer's fields. So, a Serializer with a nested field named items will try to pull the items attribute or key from an object. This is fine for a plain object with an items attribute.

However, when you try to serialize a dictionary with the same serializer, the serializer will again try to pull the items attribute from the dictionary, which turns out to be a built-in method of dict. This is why you are getting a TypeError saying that you can't iterate over a method.

The short answer to your problem is: Rename the items field to something else that isn't a built-in attribute or method of dict.

For example, the following will work:

from marshmallow import Serializer, fields, pprint

class Book(object):
    title = ''
    author = ''

class BookSerializer(Serializer):
    title = fields.String()
    author = fields.String()

class BookList(object):
    books = list()

class BookListSerializer(Serializer):
    books = fields.Nested(BookSerializer, many=True)


book1 = {'title': 'hello android', 'author': 'leejaycoke'}
book2 = {'title': 'hello iOS', 'author': 'tommy'}
book = {'books': [book1, book2]}

pprint(BookListSerializer(book).data)
# {"books": [{"author": "leejaycoke", "title": "hello android"}, {"author": "tommy", "title": "hello iOS"}]}

[leejaycoke]

Thank you very much.
I can't understand me why I'd naver tried to change attribute name (items).

[charalamm]

This answer solves the problem without having to change the key name but it may have a performance cost
#648 (comment)