python scrapy如何建模

import scrapy

class MyspiderItem(scrapy.Item):

    # define the fields for your item here like:

    name = scrapy.Field()  # 讲师的名字

    title = scrapy.Field()  # 讲师的职称

    desc = scrapy.Field()  # 讲师的介绍

# if __name__ == '__main__':

#     item = MyspiderItem()

#     item['name'] = 'lqr'  # ok

#     item['nama'] = 'lqr'  # KeyError: 'MyspiderItem does not support field: nama'