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tutorial: updating extracting data section to introduce CSS and XPath equally

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Elias Dorneles 2016-09-16 17:13:24 -03:00
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docs/intro/tutorial.rst
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@ -177,8 +177,8 @@ Scrapy to do so. This happens because :meth:`~scrapy.spiders.Spider.parse`
is Scrapy's default callback method.
Extracting Items
----------------
Extracting data
---------------
Introduction to Selectors
^^^^^^^^^^^^^^^^^^^^^^^^^
@ -191,25 +191,31 @@ mechanisms see the :ref:`Selectors documentation <topics-selectors>`.
.. _XPath: https://www.w3.org/TR/xpath
.. _CSS: https://www.w3.org/TR/selectors
Here are some examples of XPath expressions and their meanings:
Here are some examples of XPath expressions, their meanings and CSS
equivalents:
* ``/html/head/title``: selects the ``<title>`` element, inside the ``<head>``
element of an HTML document. Equivalent CSS selector: ``html > head > title``.
element of an HTML document. Using CSS, the equivalent would be: ``html >
head > title``.
* ``/html/head/title/text()``: selects the text inside the aforementioned
``<title>`` element. Equivalent CSS selector: ``html > head > title ::text``.
``<title>`` element. In Scrapy, you can do the same with CSS using ``html >
head > title::text``. The ``::text`` bit isn't really CSS, but is supported
by Scrapy for extracting purposes.
* ``//td``: selects all the ``<td>`` elements from the whole document.
Equivalent CSS selector: ``td``.
The equivalent CSS selector: ``td``.
* ``//div[@class="mine"]``: selects all ``div`` elements which contain an
attribute ``class="mine"``. Equivalent CSS selector: ``div.mine``.
* ``//div[@id="mine"]``: selects all ``div`` elements which contain an
attribute ``id="mine"``. The equivalent CSS selector would be: ``div#mine``.
These are just a couple of simple examples of what you can do with XPath, but
XPath expressions are indeed much more powerful. To learn more about XPath, we
recommend `this tutorial to learn XPath through examples
<http://zvon.org/comp/r/tut-XPath_1.html>`_, and `this tutorial to learn "how
to think in XPath" <http://plasmasturm.org/log/xpath101/>`_.
These are just a couple of simple examples of what you can do with XPath and
CSS. XPath expressions are very powerful, they're the foundation of Scrapy
selectors. In fact, CSS selectors are converted to XPath expressions
under-the-hood. To learn more about XPath, we recommend `this tutorial to learn
XPath through examples <http://zvon.org/comp/r/tut-XPath_1.html>`_, and `this
tutorial to learn "how to think in XPath"
<http://plasmasturm.org/log/xpath101/>`_.
.. note:: **CSS vs XPath:** you can go a long way extracting data from web pages
using only CSS selectors. However, XPath offers more power because besides