17 KiB
Scrapy Tutorial
In this tutorial, we'll assume that Scrapy is already installed on your system. If that's not the case, see :ref:`intro-install`.
System Message: ERROR/3 (<stdin>, line 7); backlink
Unknown interpreted text role "ref".We are going to use Open directory project (dmoz) as our example domain to scrape.
This tutorial will walk you through these tasks:
Creating a new Scrapy project
Defining the Items you will extract
Writing a :ref:`spider <topics-spiders>` to crawl a site and extract :ref:`Items <topics-items>`
System Message: ERROR/3 (<stdin>, line 17); backlink
Unknown interpreted text role "ref".
System Message: ERROR/3 (<stdin>, line 17); backlink
Unknown interpreted text role "ref".
Writing an :ref:`Item Pipeline <topics-item-pipeline>` to store the extracted Items
System Message: ERROR/3 (<stdin>, line 19); backlink
Unknown interpreted text role "ref".
Scrapy is written in Python. If you're new to the language you might want to start by getting an idea of what the language is like, to get the most out of Scrapy. If you're already familiar with other languages, and want to learn Python quickly, we recommend Dive Into Python. If you're new to programming and want to start with Python, take a look at this list of Python resources for non-programmers.
Creating a project
Before you start scraping, you will have set up a new Scrapy project. Enter a directory where you'd like to store your code and then run:
scrapy startproject tutorial
This will create a tutorial directory with the following contents:
tutorial/
scrapy.cfg
tutorial/
__init__.py
items.py
pipelines.py
settings.py
spiders/
__init__.py
...
These are basically:
- scrapy.cfg: the project configuration file
- tutorial/: the project's python module, you'll later import your code from here.
- tutorial/items.py: the project's items file.
- tutorial/pipelines.py: the project's pipelines file.
- tutorial/settings.py: the project's settings file.
- tutorial/spiders/: a directory where you'll later put your spiders.
Defining our Item
Items are containers that will be loaded with the scraped data; they work like simple python dicts but provide additional protecting against populating undeclared fields, to prevent typos.
They are declared by creating an :class:`scrapy.item.Item` class an defining its attributes as :class:`scrapy.item.Field` objects, like you will in an ORM (don't worry if you're not familiar with ORMs, you will see that this is an easy task).
System Message: ERROR/3 (<stdin>, line 71); backlink
Unknown interpreted text role "class".System Message: ERROR/3 (<stdin>, line 71); backlink
Unknown interpreted text role "class".We begin by modeling the item that we will use to hold the sites data obtained from dmoz.org, as we want to capture the name, url and description of the sites, we define fields for each of these three attributes. To do that, we edit items.py, found in the dmoz directory. Our Item class looks like this:
from scrapy.item import Item, Field
class DmozItem(Item):
title = Field()
link = Field()
desc = Field()
This may seem complicated at first, but defining the item allows you to use other handy components of Scrapy that need to know how your item looks like.
Our first Spider
Spiders are user-written classes used to scrape information from a domain (or group of domains).
They define an initial list of URLs to download, how to follow links, and how to parse the contents of those pages to extract :ref:`items <topics-items>`.
System Message: ERROR/3 (<stdin>, line 97); backlink
Unknown interpreted text role "ref".To create a Spider, you must subclass :class:`scrapy.spider.BaseSpider`, and define the three main, mandatory, attributes:
System Message: ERROR/3 (<stdin>, line 100); backlink
Unknown interpreted text role "class".:attr:`~scrapy.spider.BaseSpider.name`: identifies the Spider. It must be unique, that is, you can't set the same name for different Spiders.
System Message: ERROR/3 (<stdin>, line 103); backlink
Unknown interpreted text role "attr".
:attr:`~scrapy.spider.BaseSpider.start_urls`: is a list of URLs where the Spider will begin to crawl from. So, the first pages downloaded will be those listed here. The subsequent URLs will be generated successively from data contained in the start URLs.
System Message: ERROR/3 (<stdin>, line 106); backlink
Unknown interpreted text role "attr".
:meth:`~scrapy.spider.BaseSpider.parse` is a method of the spider, which will be called with the downloaded :class:`~scrapy.http.Response` object of each start URL. The response is passed to the method as the first and only argument.
System Message: ERROR/3 (<stdin>, line 111); backlink
Unknown interpreted text role "meth".
System Message: ERROR/3 (<stdin>, line 111); backlink
Unknown interpreted text role "class".
This method is responsible for parsing the response data and extracting scraped data (as scraped items) and more URLs to follow.
The :meth:`~scrapy.spider.BaseSpider.parse` method is in charge of processing the response and returning scraped data (as :class:`~scrapy.item.Item` objects) and more URLs to follow (as :class:`~scrapy.http.Request` objects).
System Message: ERROR/3 (<stdin>, line 119); backlink
Unknown interpreted text role "meth".
System Message: ERROR/3 (<stdin>, line 119); backlink
Unknown interpreted text role "class".
System Message: ERROR/3 (<stdin>, line 119); backlink
Unknown interpreted text role "class".
This is the code for our first Spider; save it in a file named dmoz_spider.py under the dmoz/spiders directory:
from scrapy.spider import BaseSpider
class DmozSpider(BaseSpider):
name = "dmoz"
allowed_domains = ["dmoz.org"]
start_urls = [
"http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
"http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
]
def parse(self, response):
filename = response.url.split("/")[-2]
open(filename, 'wb').write(response.body)
Crawling
To put our spider to work, go to the project's top level directory and run:
scrapy crawl dmoz
The crawl dmoz command runs the spider for the dmoz.org domain. You will get an output similar to this:
2008-08-20 03:51:13-0300 [scrapy] INFO: Started project: dmoz 2008-08-20 03:51:13-0300 [tutorial] INFO: Enabled extensions: ... 2008-08-20 03:51:13-0300 [tutorial] INFO: Enabled downloader middlewares: ... 2008-08-20 03:51:13-0300 [tutorial] INFO: Enabled spider middlewares: ... 2008-08-20 03:51:13-0300 [tutorial] INFO: Enabled item pipelines: ... 2008-08-20 03:51:14-0300 [dmoz] INFO: Spider opened 2008-08-20 03:51:14-0300 [dmoz] DEBUG: Crawled <http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/> (referer: <None>) 2008-08-20 03:51:14-0300 [dmoz] DEBUG: Crawled <http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> (referer: <None>) 2008-08-20 03:51:14-0300 [dmoz] INFO: Spider closed (finished)
Pay attention to the lines containing [dmoz], which corresponds to our spider. You can see a log line for each URL defined in start_urls. Because these URLs are the starting ones, they have no referrers, which is shown at the end of the log line, where it says (referer: <None>).
But more interesting, as our parse method instructs, two files have been created: Books and Resources, with the content of both URLs.
What just happened under the hood?
Scrapy creates :class:`scrapy.http.Request` objects for each URL in the start_urls attribute of the Spider, and assigns them the parse method of the spider as their callback function.
System Message: ERROR/3 (<stdin>, line 171); backlink
Unknown interpreted text role "class".These Requests are scheduled, then executed, and :class:`scrapy.http.Response` objects are returned and then fed back to the spider, through the :meth:`~scrapy.spider.BaseSpider.parse` method.
System Message: ERROR/3 (<stdin>, line 175); backlink
Unknown interpreted text role "class".System Message: ERROR/3 (<stdin>, line 175); backlink
Unknown interpreted text role "meth".Extracting Items
Introduction to Selectors
There are several ways to extract data from web pages. Scrapy uses a mechanism based on XPath expressions called :ref:`XPath selectors <topics-selectors>`. For more information about selectors and other extraction mechanisms see the :ref:`XPath selectors documentation <topics-selectors>`.
System Message: ERROR/3 (<stdin>, line 185); backlink
Unknown interpreted text role "ref".System Message: ERROR/3 (<stdin>, line 185); backlink
Unknown interpreted text role "ref".Here are some examples of XPath expressions and their meanings:
- /html/head/title: selects the <title> element, inside the <head> element of a HTML document
- /html/head/title/text(): selects the text inside the aforementioned <title> element.
- //td: selects all the <td> elements
- //div[@class="mine"]: selects all div elements which contain an attribute class="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 XPath tutorial.
For working with XPaths, Scrapy provides a :class:`~scrapy.selector.XPathSelector` class, which comes in two flavours, :class:`~scrapy.selector.HtmlXPathSelector` (for HTML data) and :class:`~scrapy.selector.XmlXPathSelector` (for XML data). In order to use them you must instantiate the desired class with a :class:`~scrapy.http.Response` object.
System Message: ERROR/3 (<stdin>, line 209); backlink
Unknown interpreted text role "class".System Message: ERROR/3 (<stdin>, line 209); backlink
Unknown interpreted text role "class".System Message: ERROR/3 (<stdin>, line 209); backlink
Unknown interpreted text role "class".System Message: ERROR/3 (<stdin>, line 209); backlink
Unknown interpreted text role "class".You can see selectors as objects that represent nodes in the document structure. So, the first instantiated selectors are associated to the root node, or the entire document.
Selectors have three methods (click on the method to see the complete API documentation).
:meth:`~scrapy.selector.XPathSelector.select`: returns a list of selectors, each of them representing the nodes selected by the xpath expression given as argument.
System Message: ERROR/3 (<stdin>, line 222); backlink
Unknown interpreted text role "meth".
- :meth:`~scrapy.selector.XPathSelector.extract`: returns a unicode string with
System Message: ERROR/3 (<stdin>, line 227); backlink
Unknown interpreted text role "meth".
the data selected by the XPath selector.
:meth:`~scrapy.selector.XPathSelector.re`: returns a list of unicode strings extracted by applying the regular expression given as argument.
System Message: ERROR/3 (<stdin>, line 229); backlink
Unknown interpreted text role "meth".
Trying Selectors in the Shell
To illustrate the use of Selectors we're going to use the built-in :ref:`Scrapy shell <topics-shell>`, which also requires IPython (an extended Python console) installed on your system.
System Message: ERROR/3 (<stdin>, line 236); backlink
Unknown interpreted text role "ref".To start a shell, you must go to the project's top level directory and run:
scrapy shell http://www.dmoz.org/Computers/Programming/Languages/Python/Books/
This is what the shell looks like:
[ ... Scrapy log here ... ] [s] Available Scrapy objects: [s] 2010-08-19 21:45:59-0300 [default] INFO: Spider closed (finished) [s] hxs <HtmlXPathSelector (http://www.dmoz.org/Computers/Programming/Languages/Python/Books/) xpath=None> [s] item Item() [s] request <GET http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> [s] response <200 http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> [s] spider <BaseSpider 'default' at 0x1b6c2d0> [s] xxs <XmlXPathSelector (http://www.dmoz.org/Computers/Programming/Languages/Python/Books/) xpath=None> [s] Useful shortcuts: [s] shelp() Print this help [s] fetch(req_or_url) Fetch a new request or URL and update shell objects [s] view(response) View response in a browser In [1]:
After the shell loads, you will have the response fetched in a local response variable, so if you type response.body you will see the body of the response, or you can type response.headers to see its headers.
The shell also instantiates two selectors, one for HTML (in the hxs variable) and one for XML (in the xxs variable) with this response. So let's try them:
In [1]: hxs.select('/html/head/title')
Out[1]: [<HtmlXPathSelector (title) xpath=/html/head/title>]
In [2]: hxs.select('/html/head/title').extract()
Out[2]: [u'<title>Open Directory - Computers: Programming: Languages: Python: Books</title>']
In [3]: hxs.select('/html/head/title/text()')
Out[3]: [<HtmlXPathSelector (text) xpath=/html/head/title/text()>]
In [4]: hxs.select('/html/head/title/text()').extract()
Out[4]: [u'Open Directory - Computers: Programming: Languages: Python: Books']
In [5]: hxs.select('/html/head/title/text()').re('(\w+):')
Out[5]: [u'Computers', u'Programming', u'Languages', u'Python']
Extracting the data
Now, let's try to extract some real information from those pages.
You could type response.body in the console, and inspect the source code to figure out the XPaths you need to use. However, inspecting the raw HTML code there could become a very tedious task. To make this an easier task, you can use some Firefox extensions like Firebug. For more information see :ref:`topics-firebug` and :ref:`topics-firefox`.
System Message: ERROR/3 (<stdin>, line 291); backlink
Unknown interpreted text role "ref".System Message: ERROR/3 (<stdin>, line 291); backlink
Unknown interpreted text role "ref".After inspecting the page source, you'll find that the web sites information is inside a <ul> element, in fact the second <ul> element.
So we can select each <li> element belonging to the sites list with this code:
hxs.select('//ul/li')
And from them, the sites descriptions:
hxs.select('//ul/li/text()').extract()
The sites titles:
hxs.select('//ul/li/a/text()').extract()
And the sites links:
hxs.select('//ul/li/a/@href').extract()
As we said before, each select() call returns a list of selectors, so we can concatenate further select() calls to dig deeper into a node. We are going to use that property here, so:
sites = hxs.select('//ul/li')
for site in sites:
title = site.select('a/text()').extract()
link = site.select('a/@href').extract()
desc = site.select('text()').extract()
print title, link, desc
Note
For a more detailed description of using nested selectors, see :ref:`topics-selectors-nesting-selectors` and :ref:`topics-selectors-relative-xpaths` in the :ref:`topics-selectors` documentation
System Message: ERROR/3 (<stdin>, line 330); backlink
Unknown interpreted text role "ref".System Message: ERROR/3 (<stdin>, line 330); backlink
Unknown interpreted text role "ref".System Message: ERROR/3 (<stdin>, line 330); backlink
Unknown interpreted text role "ref".Let's add this code to our spider:
from scrapy.spider import BaseSpider
from scrapy.selector import HtmlXPathSelector
class DmozSpider(BaseSpider):
name = "dmoz"
allowed_domains = ["dmoz.org"]
start_urls = [
"http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
"http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
]
def parse(self, response):
hxs = HtmlXPathSelector(response)
sites = hxs.select('//ul/li')
for site in sites:
title = site.select('a/text()').extract()
link = site.select('a/@href').extract()
desc = site.select('text()').extract()
print title, link, desc
Now try crawling the dmoz.org domain again and you'll see sites being printed in your output, run:
scrapy crawl dmoz
Using our item
:class:`~scrapy.item.Item` objects are custom python dicts; you can access the values of their fields (attributes of the class we defined earlier) using the standard dict syntax like:
System Message: ERROR/3 (<stdin>, line 365); backlink
Unknown interpreted text role "class".>>> item = DmozItem() >>> item['title'] = 'Example title' >>> item['title'] 'Example title'
Spiders are expected to return their scraped data inside :class:`~scrapy.item.Item` objects. So, in order to returnthe data we've scraped so far, the final code for our Spider would be like this:
System Message: ERROR/3 (<stdin>, line 374); backlink
Unknown interpreted text role "class".from scrapy.spider import BaseSpider
from scrapy.selector import HtmlXPathSelector
from tutorial.items import DmozItem
class DmozSpider(BaseSpider):
name = "dmoz"
allowed_domains = ["dmoz.org"]
start_urls = [
"http://www.dmoz.org/Computers/Programming/Languages/Python/Books/",
"http://www.dmoz.org/Computers/Programming/Languages/Python/Resources/"
]
def parse(self, response):
hxs = HtmlXPathSelector(response)
sites = hxs.select('//ul/li')
items = []
for site in sites:
item = DmozItem()
item['title'] = site.select('a/text()').extract()
item['link'] = site.select('a/@href').extract()
item['desc'] = site.select('text()').extract()
items.append(item)
return items
Note
You can find a fully-functional variant of this spider in the dirbot project available at https://github.com/scrapy/dirbot
Now doing a crawl on the dmoz.org domain yields DmozItem's:
[dmoz] DEBUG: Scraped DmozItem(desc=[u' - By David Mertz; Addison Wesley. Book in progress, full text, ASCII format. Asks for feedback. [author website, Gnosis Software, Inc.]\n'], link=[u'http://gnosis.cx/TPiP/'], title=[u'Text Processing in Python']) in <http://www.dmoz.org/Computers/Programming/Languages/Python/Books/> [dmoz] DEBUG: Scraped DmozItem(desc=[u' - By Sean McGrath; Prentice Hall PTR, 2000, ISBN 0130211192, has CD-ROM. Methods to build XML applications fast, Python tutorial, DOM and SAX, new Pyxie open source XML processing library. [Prentice Hall PTR]\n'], link=[u'http://www.informit.com/store/product.aspx?isbn=0130211192'], title=[u'XML Processing with Python']) in <http://www.dmoz.org/Computers/Programming/Languages/Python/Books/>
Storing the scraped data
The simplest way to store the scraped data is by using the :ref:`Feed exports <topics-feed-exports>`, with the following command:
System Message: ERROR/3 (<stdin>, line 414); backlink
Unknown interpreted text role "ref".scrapy crawl dmoz --set FEED_URI=items.json --set FEED_FORMAT=json
That will generate a items.json file containing all scraped items, serialized in JSON.
In small projects (like the one in this tutorial), that should be enough. However, if you want to perform more complex things with the scraped items, you can write an :ref:`Item Pipeline <topics-item-pipeline>`. As with Items, a placeholder file for Item Pipelines has been set up for you when the project is created, in tutorial/pipelines.py. Though you don't need to implement any item pipeline if you just want to store the scraped items.
System Message: ERROR/3 (<stdin>, line 422); backlink
Unknown interpreted text role "ref".Next steps
This tutorial covers only the basics of Scrapy, but there's a lot of other features not mentioned here. We recommend you continue by playing with an example project (see :ref:`intro-examples`), and then continue with the section :ref:`section-basics`.
System Message: ERROR/3 (<stdin>, line 432); backlink
Unknown interpreted text role "ref".System Message: ERROR/3 (<stdin>, line 432); backlink
Unknown interpreted text role "ref".