1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
.. currentmodule:: itemloaders
.. _declaring-loaders:
Declaring Item Loaders
======================
Item Loaders are declared by using a class definition syntax. Here is an example::
from itemloaders import ItemLoader
from itemloaders.processors import TakeFirst, MapCompose, Join
class ProductLoader(ItemLoader):
default_output_processor = TakeFirst()
name_in = MapCompose(str.title)
name_out = Join()
# using a built-in processor
price_in = MapCompose(str.strip)
# using a function
def price_out(self, values):
return float(values[0])
loader = ProductLoader()
loader.add_value('name', 'plasma TV')
loader.add_value('price', '999.98')
loader.load_item()
# {'name': 'Plasma Tv', 'price': 999.98}
As you can see, input processors are declared using the ``_in`` suffix while
output processors are declared using the ``_out`` suffix. And you can also
declare a default input/output processors using the
:attr:`ItemLoader.default_input_processor` and
:attr:`ItemLoader.default_output_processor` attributes.
The precedence order, for both input and output processors, is as follows:
1. Item Loader field-specific attributes: ``field_in`` and ``field_out`` (most
precedence)
2. Field metadata (``input_processor`` and ``output_processor`` keys).
Check out `itemadapter field metadata
<https://github.com/scrapy/itemadapter#metadata-support>`_ for more
information.
.. versionadded:: 1.0.1
3. Item Loader defaults: :meth:`ItemLoader.default_input_processor` and
:meth:`ItemLoader.default_output_processor` (least precedence)
See also: :ref:`extending-loaders`.
|
