# 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 `ItemLoader.default_input_processor` and `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 for more information.

   Added in version 1.0.1.

3. Item Loader defaults: `ItemLoader.default_input_processor()` and `ItemLoader.default_output_processor()` (least precedence)

See also: Reusing and extending Item Loaders.