10 KiB
Frequently Asked Questions
How does Scrapy compare to BeautifulSoup or lxml?
BeautifulSoup and lxml are libraries for parsing HTML and XML. Scrapy is an application framework for writing web spiders that crawl web sites and extract data from them.
Scrapy provides a built-in mechanism for extracting data (called :ref:`selectors <topics-selectors>`) but you can easily use BeautifulSoup (or lxml) instead, if you feel more comfortable working with them. After all, they're just parsing libraries which can be imported and used from any Python code.
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Unknown interpreted text role "ref".In other words, comparing BeautifulSoup (or lxml) to Scrapy is like comparing jinja2 to Django.
What Python versions does Scrapy support?
Scrapy runs in Python 2.6 and 2.7.
Does Scrapy work with Python 3.0?
No, and there are no plans to port Scrapy to Python 3.0 yet. At the moment, Scrapy works with Python 2.6 and 2.7.
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.. seealso:: :ref:`faq-python-versions`.
Did Scrapy "steal" X from Django?
Probably, but we don't like that word. We think Django is a great open source project and an example to follow, so we've used it as an inspiration for Scrapy.
We believe that, if something is already done well, there's no need to reinvent it. This concept, besides being one of the foundations for open source and free software, not only applies to software but also to documentation, procedures, policies, etc. So, instead of going through each problem ourselves, we choose to copy ideas from those projects that have already solved them properly, and focus on the real problems we need to solve.
We'd be proud if Scrapy serves as an inspiration for other projects. Feel free to steal from us!
Does Scrapy work with HTTP proxies?
Yes. Support for HTTP proxies is provided (since Scrapy 0.8) through the HTTP Proxy downloader middleware. See :class:`~scrapy.contrib.downloadermiddleware.httpproxy.HttpProxyMiddleware`.
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Unknown interpreted text role "class".Scrapy crashes with: ImportError: No module named win32api
You need to install pywin32 because of this Twisted bug.
How can I simulate a user login in my spider?
See :ref:`topics-request-response-ref-request-userlogin`.
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Unknown interpreted text role "ref".Does Scrapy crawl in breath-first or depth-first order?
By default, Scrapy uses a LIFO queue for storing pending requests, which basically means that it crawls in DFO order. This order is more convenient in most cases. If you do want to crawl in true BFO order, you can do it by setting the following settings:
DEPTH_PRIORITY = 1 SCHEDULER_DISK_QUEUE = 'scrapy.squeue.PickleFifoDiskQueue' SCHEDULER_MEMORY_QUEUE = 'scrapy.squeue.FifoMemoryQueue'
My Scrapy crawler has memory leaks. What can I do?
See :ref:`topics-leaks`.
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Unknown interpreted text role "ref".Also, Python has a builtin memory leak issue which is described in :ref:`topics-leaks-without-leaks`.
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Unknown interpreted text role "ref".How can I make Scrapy consume less memory?
See previous question.
Can I use Basic HTTP Authentication in my spiders?
Yes, see :class:`~scrapy.contrib.downloadermiddleware.httpauth.HttpAuthMiddleware`.
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Unknown interpreted text role "class".Why does Scrapy download pages in English instead of my native language?
Try changing the default Accept-Language request header by overriding the :setting:`DEFAULT_REQUEST_HEADERS` setting.
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Unknown interpreted text role "setting".Where can I find some example Scrapy projects?
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Unknown interpreted text role "ref".Can I run a spider without creating a project?
Yes. You can use the :command:`runspider` command. For example, if you have a spider written in a my_spider.py file you can run it with:
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See :command:`runspider` command for more info.
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Unknown interpreted text role "command".I get "Filtered offsite request" messages. How can I fix them?
Those messages (logged with DEBUG level) don't necessarily mean there is a problem, so you may not need to fix them.
Those message are thrown by the Offsite Spider Middleware, which is a spider middleware (enabled by default) whose purpose is to filter out requests to domains outside the ones covered by the spider.
For more info see: :class:`~scrapy.contrib.spidermiddleware.offsite.OffsiteMiddleware`.
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Unknown interpreted text role "class".What is the recommended way to deploy a Scrapy crawler in production?
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Unknown interpreted text role "ref".Can I use JSON for large exports?
It'll depend on how large your output is. See :ref:`this warning <json-with-large-data>` in :class:`~scrapy.contrib.exporter.JsonItemExporter` documentation.
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Unknown interpreted text role "class".Can I return (Twisted) deferreds from signal handlers?
Some signals support returning deferreds from their handlers, others don't. See the :ref:`topics-signals-ref` to know which ones.
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Unknown interpreted text role "ref".What does the response status code 999 means?
999 is a custom reponse status code used by Yahoo sites to throttle requests. Try slowing down the crawling speed by using a download delay of 2 (or higher) in your spider:
class MySpider(CrawlSpider):
name = 'myspider'
DOWNLOAD_DELAY = 2
# [ ... rest of the spider code ... ]
Or by setting a global download delay in your project with the :setting:`DOWNLOAD_DELAY` setting.
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Unknown interpreted text role "setting".Can I call pdb.set_trace() from my spiders to debug them?
Yes, but you can also use the Scrapy shell which allows you too quickly analyze (and even modify) the response being processed by your spider, which is, quite often, more useful than plain old pdb.set_trace().
For more info see :ref:`topics-shell-inspect-response`.
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Unknown interpreted text role "ref".Simplest way to dump all my scraped items into a JSON/CSV/XML file?
To dump into a JSON file:
scrapy crawl myspider -o items.json -t json
To dump into a CSV file:
scrapy crawl myspider -o items.csv -t csv
To dump into a XML file:
scrapy crawl myspider -o items.xml -t xml
For more information see :ref:`topics-feed-exports`
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Unknown interpreted text role "ref".What's this huge cryptic __VIEWSTATE parameter used in some forms?
The __VIEWSTATE parameter is used in sites built with ASP.NET/VB.NET. For more info on how it works see this page. Also, here's an example spider which scrapes one of these sites.
What's the best way to parse big XML/CSV data feeds?
Parsing big feeds with XPath selectors can be problematic since they need to build the DOM of the entire feed in memory, and this can be quite slow and consume a lot of memory.
In order to avoid parsing all the entire feed at once in memory, you can use the functions xmliter and csviter from scrapy.utils.iterators module. In fact, this is what the feed spiders (see :ref:`topics-spiders`) use under the cover.
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Unknown interpreted text role "ref".How can I instruct a spider to stop itself?
Raise the :exc:`~scrapy.exceptions.CloseSpider` exception from a callback. For more info see: :exc:`~scrapy.exceptions.CloseSpider`.
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Unknown interpreted text role "exc".How can I prevent my Scrapy bot from getting banned?
Some websites implement certain measures to prevent bots from crawling them, with varying degrees of sophistication. Getting around those measures can be difficult and tricky, and may sometimes require special infrastructure.
Here are some tips to keep in mind when dealing with these kind of sites:
rotate your user agent from a pool of well-known ones from browsers (google around to get a list of them)
disable cookies (see :setting:`COOKIES_ENABLED`) as some sites may use cookies to spot bot behaviour
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use download delays (2 or higher). See :setting:`DOWNLOAD_DELAY` setting.
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is possible, use Google cache to fetch pages, instead of hitting the sites directly
use a pool of rotating IPs. For example, the free Tor project.
If you are still unable to prevent your bot getting banned, consider contacting commercial support.