Unexpected behaviour while adding scrapy.Item sub class as a value to itemloader.

[HassanQamar07]

Sample code

import scrapy
from itemloaders import ItemLoader
from itemloaders.processors import Identity


class TestItem1(scrapy.Item):
    list_of_test_items = scrapy.Field()


class TestItem2(scrapy.Item):
    count = scrapy.Field()
    price = scrapy.Field()


class TestItemLoader(ItemLoader):
    default_item_class = TestItem1

    list_of_test_items_in = Identity()
    list_of_test_items_out = Identity()


il = TestItemLoader()
il.add_value('list_of_test_items', TestItem2(count=1, price=50))
print(il.load_item())

Expected output

{'list_of_test_items': [{'count': 1, 'price': 50}]}

Actual output

{'list_of_test_items': ['count', 'price']}

This is because the _BaseItem is removed from _ITERABLE_SINGLE_VALUES https://github.com/scrapy/itemloaders/blob/master/itemloaders/utils.py#L9

In scrapy _BaseItem is included in _ITERABLE_SINGLE_VALUES https://github.com/scrapy/scrapy/blob/2.2/scrapy/utils/misc.py#L20