scrapy - item loader - default processors

Question

I'm new to python and scrapy, so I apologise for maybe silly questions in advance. I have some troubles with default item loader's processors, and related questions:

1. I use default_input_processor variable to extract first value from list using TakeFirst() processor like that:

   class    CaseLoader(scrapy.loader.ItemLoader):
       default_input_processor = TakeFirst()
   

   and usage:

     def load_row_data(self, row):
         cl = CaseLoader(CaseItem(), row)
   
         cl.add_xpath('case_num',  './/td[1]/a/text()')
         cl.add_xpath('case_link', './/td[1]/a/@href')
         cl.add_xpath('name',      './/td[3]/text()')
         return cl.load_item()
   

   then I yield this item from callback methos, but TakeFirst() doesn't work, I get a list instead of string. If I use TakeFist() as default_output_processor, it works. How does default_input_processor works? Why TakeFisrt() processor isn't applied in this case?

2. In documentation I saw usage of unicode.strip method:

   from scrapy.loader import ItemLoader
   from scrapy.loader.processors import TakeFirst, MapCompose, Join
   
   class ProductLoader(ItemLoader):
   
       default_output_processor = TakeFirst()
   
       name_in = MapCompose(unicode.title)
       name_out = Join()
   
       rice_in = MapCompose(unicode.strip)
   
       # ...
   

   But when I tried to use it in my Item Loader in Compose() I get error:

   NameError: name 'unicode' is not defined
   

   If I understand right this method should remove white spaces from beginning and end of the string. How to use it properly? Do I need to code and use my strip function instead?

Answer 1

That is because the documentation is using Python2 and you are using Python3

There is no unicode in Python3. You should use str instead

class ProductLoader(ItemLoader):

    default_output_processor = TakeFirst()

    name_in = MapCompose(str.title)
    name_out = Join()

    rice_in = MapCompose(str.strip)

See below thread also for more information

NameError: global name 'unicode' is not defined - in Python 3