======= ============================== SEP 5 Title ItemBuilder API Author Ismael Carnales, Pablo Hoffman Created 2009-07-24 Status Obsoleted by :doc:sep-008 ======= ==============================

========================================= SEP-005: Detailed ItemBuilder API use

Item class for examples:

.. code-block:: python

#!python class NewsItem(Item): url = fields.TextField() headline = fields.TextField() content = fields.TextField() published = fields.DateField()

gSetting expanders

.. code-block:: python

#!python class NewsItemBuilder(ItemBuilder): item_class = NewsItem

   headline = reducers.Reducer(extract, remove_tags(), unquote(), strip)

This approach will override the Reducer class for BuilderFields depending on their Item Field class:

• MultivaluedField = PassValue
• TextField = JoinStrings
• other = TakeFirst

gSetting reducers

.. code-block:: python

#!python class NewsItemBuilder(ItemBuilder): item_class = NewsItem

   headline = reducers.TakeFirst(extract, remove_tags(), unquote(), strip)
   published = reducers.Reducer(extract, remove_tags(), unquote(), strip)

As with the previous example this would select join_strings as the reducer for content

gSetting expanders/reducers new way

.. code-block:: python

#!python class NewsItemBuilder(ItemBuilder): item_class = NewsItem

   headline = BuilderField(extract, remove_tags(), unquote(), strip)
   content = BuilderField(extract, remove_tags(), unquote(), strip)

   class Reducer:
       headline = TakeFirst

gExtending ItemBuilder

.. code-block:: python

#!python class SiteNewsItemBuilder(NewsItemBuilder): published = reducers.Reducer( extract, remove_tags(), unquote(), strip, to_date("%d.%m.%Y") )

gExtending ItemBuilder using statich methods

.. code-block:: python

#!python class SiteNewsItemBuilder(NewsItemBuilder): published = reducers.Reducer(NewsItemBuilder.published, to_date("%d.%m.%Y"))

gUsing default_builder

.. code-block:: python

#!python class DefaultedNewsItemBuilder(ItemBuilder): item_class = NewsItem

   default_builder = reducers.Reducer(extract, remove_tags(), unquote(), strip)

This will use default_builder as the builder for every field in the item class. As a reducer is not set reducers will be set based on Item Field classes.

gReset default_builder for a field

.. code-block:: python

#!python class DefaultedNewsItemBuilder(ItemBuilder): item_class = NewsItem

   default_builder = reducers.Reducer(extract, remove_tags(), unquote(), strip)
   url = BuilderField()

gExtending default ItemBuilder

.. code-block:: python

#!python class SiteNewsItemBuilder(NewsItemBuilder): published = reducers.Reducer( extract, remove_tags(), unquote(), strip, to_date("%d.%m.%Y") )

gExtending default ItemBuilder using static methods

.. code-block:: python

#!python class SiteNewsItemBuilder(NewsItemBuilder): published = reducers.Reducer(NewsItemBuilder.default_builder, to_date("%d.%m.%Y"))