4.6 KiB
Item Fields
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.. module:: scrapy.newitem.fields
Field options
Every Field class constructor accepts these arguments.
default
The default value for the field. See :ref:`topics-newitem-index-defaults`.
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These are the available built-in Field types. See :ref:`ref-newitem-fields-custom-fields` for info on creating your own field types.
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A unicode text.
This class overrides the following methods from :class:`BaseField`:
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.. method:: from_unicode_list(unicode_list) Return a unicode string composed by joining the elements of ``unicode_list`` with spaces. For more info about this method see :class:`BaseField.from_unicode_list`.
IntegerField
An integer.
DecimalField
A fixed-precision decimal number, represented in Python by a Decimal instance.
FloatField
A floating-point number represented in Python by a float instance.
BooleanField
A boolean (true/false) field.
DateTimeField
A date with time, represented in Python by a datetime.datetime instance.
DateField
A date, represented in Python by a datetime.date instance.
TimeField
A time, represented in Python by a datetime.time instance.
Creating custom fields
All field classes are subclasses of the :class:`BaseField` class (see below) which you can also subclass to create your own custom fields.
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The base class for all fields. It only provides code for handling default values, not any particular type. It cannot be used directly either, as its :meth:`BaseField.to_python` method is not implemented.
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class NewsItem(Item):
content = fields.TextField() # correct, no default value
author = fields.TextField(default=u'Myself") # correct, with default value
published = fields.DateField(default=23) # wrong default type (will raise TypeError)
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.. method:: to_python(value)
Convert the input value to the type expected by this field and return
it.
For example, :class:`IntegerField` would convert ``'1'`` to ``1``, while
:class:`DecimalField` would convert ``'1'`` to ``Decimal('1')`` and so
on.
This method is not implemented in the :class:`BaseField` class, so it
must always be implemented in all its subclasses, in order to be usable.
This method should raise ``TypeError`` if the input type is not
supported, and ``ValueError`` if the input type is support but its value
is not appropriate (for example, an integer outside a given range).
This method must always return object of the expected field type.
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.. method:: from_unicode_list(unicode_list)
Take the input list of unicode strings and convert it to a proper value
with the type expected by this field. If no proper value if found,
``None`` is returned instead.
The default behaviour is to return the value of the first item of the
list, passed through the :meth:`to_python` method, or ``None`` if the
list is empty::
return self.to_python(unicode_list[0]) if unicode_list else None
This default behaviour is provided because it's the more common one, but
it's typical for :class:`BaseField` subclasses to override this method,
such as the :meth:`TextField.from_unicode_list` method.
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.. method:: get_default() Return the default value for this field, or ``None`` if the field doesn't specify any.