RomanNum3ral
/
scrapy
mirror of https://github.com/scrapy/scrapy.git
1
0
Fork 0
Code Issues Packages Projects Releases Wiki Activity
scrapy/docs/topics/shell.rst

11 KiB
Raw Permalink Blame History

<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> <head> </head>

Scrapy shell

The Scrapy shell is an interactive shell where you can try and debug your scraping code very quickly, without having to run the spider. It's meant to be used for testing data extraction code, but you can actually use it for testing any kind of code as it is also a regular Python shell.

The shell is used for testing XPath or CSS expressions and see how they work and what data they extract from the web pages you're trying to scrape. It allows you to interactively test your expressions while you're writing your spider, without having to run the spider to test every change.

Once you get familiarized with the Scrapy shell, you'll see that it's an invaluable tool for developing and debugging your spiders.

Configuring the shell

If you have IPython installed, the Scrapy shell will use it (instead of the standard Python console). The IPython console is much more powerful and provides smart auto-completion and colorized output, among other things.

We highly recommend you install IPython, especially if you're working on Unix systems (where IPython excels). See the IPython installation guide for more info.

Scrapy also has support for bpython, and will try to use it where IPython is unavailable.

Through Scrapy's settings you can configure it to use any one of ipython, bpython or the standard python shell, regardless of which are installed. This is done by setting the SCRAPY_PYTHON_SHELL environment variable; or by defining it in your :ref:`scrapy.cfg <topics-config-settings>`:

System Message: ERROR/3 (<stdin>, line 34); backlink

Unknown interpreted text role "ref".
[settings]
shell = bpython

Launch the shell

To launch the Scrapy shell you can use the :command:`shell` command like this:

System Message: ERROR/3 (<stdin>, line 49); backlink

Unknown interpreted text role "command".
scrapy shell <url>

Where the <url> is the URL you want to scrape.

:command:`shell` also works for local files. This can be handy if you want to play around with a local copy of a web page. :command:`shell` understands the following syntaxes for local files:

System Message: ERROR/3 (<stdin>, line 56); backlink

Unknown interpreted text role "command".

System Message: ERROR/3 (<stdin>, line 56); backlink

Unknown interpreted text role "command".
# UNIX-style
scrapy shell ./path/to/file.html
scrapy shell ../other/path/to/file.html
scrapy shell /absolute/path/to/file.html

# File URI
scrapy shell file:///absolute/path/to/file.html

Note

When using relative file paths, be explicit and prepend them with ./ (or ../ when relevant). scrapy shell index.html will not work as one might expect (and this is by design, not a bug).

Because :command:`shell` favors HTTP URLs over File URIs, and index.html being syntactically similar to example.com, :command:`shell` will treat index.html as a domain name and trigger a DNS lookup error:

System Message: ERROR/3 (<stdin>, line 73); backlink

Unknown interpreted text role "command".

System Message: ERROR/3 (<stdin>, line 73); backlink

Unknown interpreted text role "command".
$ scrapy shell index.html
[ ... scrapy shell starts ... ]
[ ... traceback ... ]
twisted.internet.error.DNSLookupError: DNS lookup failed:
address 'index.html' not found: [Errno -5] No address associated with hostname.

:command:`shell` will not test beforehand if a file called index.html exists in the current directory. Again, be explicit.

System Message: ERROR/3 (<stdin>, line 84); backlink

Unknown interpreted text role "command".

Using the shell

The Scrapy shell is just a regular Python console (or IPython console if you have it available) which provides some additional shortcut functions for convenience.

Available Shortcuts

  • shelp() - print a help with the list of available objects and shortcuts
  • fetch(url[, redirect=True]) - fetch a new response from the given URL and update all related objects accordingly. You can optionally ask for HTTP 3xx redirections to not be followed by passing redirect=False
  • fetch(request) - fetch a new response from the given request and update all related objects accordingly.
  • view(response) - open the given response in your local web browser, for inspection. This will add a <base> tag to the response body in order for external links (such as images and style sheets) to display properly. Note, however, that this will create a temporary file in your computer, which won't be removed automatically.

Available Scrapy objects

The Scrapy shell automatically creates some convenient objects from the downloaded page, like the :class:`~scrapy.http.Response` object and the :class:`~scrapy.Selector` objects (for both HTML and XML content).

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".

Those objects are:

Example of shell session

Here's an example of a typical shell session where we start by scraping the https://www.scrapy.org/ page, and then proceed to scrape the https://old.reddit.com/ page. Finally, we modify the (Reddit) request method to POST and re-fetch it getting an error. We end the session by typing Ctrl-D (in Unix systems) or Ctrl-Z in Windows.

Keep in mind that the data extracted here may not be the same when you try it, as those pages are not static and could have changed by the time you test this. The only purpose of this example is to get you familiarized with how the Scrapy shell works.

First, we launch the shell:

scrapy shell 'https://scrapy.org' --nolog

Note

Remember to always enclose URLs in quotes when running the Scrapy shell from the command line, otherwise URLs containing arguments (i.e. the & character) will not work.

On Windows, use double quotes instead:

scrapy shell "https://scrapy.org" --nolog

Then, the shell fetches the URL (using the Scrapy downloader) and prints the list of available objects and useful shortcuts (you'll notice that these lines all start with the [s] prefix):

[s] Available Scrapy objects:
[s]   scrapy     scrapy module (contains scrapy.Request, scrapy.Selector, etc)
[s]   crawler    <scrapy.crawler.Crawler object at 0x7f07395dd690>
[s]   item       {}
[s]   request    <GET https://scrapy.org>
[s]   response   <200 https://scrapy.org/>
[s]   settings   <scrapy.settings.Settings object at 0x7f07395dd710>
[s]   spider     <DefaultSpider 'default' at 0x7f0735891690>
[s] Useful shortcuts:
[s]   fetch(url[, redirect=True]) Fetch URL and update local objects (by default, redirects are followed)
[s]   fetch(req)                  Fetch a scrapy.Request and update local objects
[s]   shelp()           Shell help (print this help)
[s]   view(response)    View response in a browser

>>>

After that, we can start playing with the objects:

System Message: WARNING/2 (<stdin>, line 196)

Cannot analyze code. Pygments package not found.

.. code-block:: pycon

    >>> response.xpath("//title/text()").get()
    'Scrapy | A Fast and Powerful Scraping and Web Crawling Framework'

    >>> fetch("https://old.reddit.com/")

    >>> response.xpath("//title/text()").get()
    'reddit: the front page of the internet'

    >>> request = request.replace(method="POST")

    >>> fetch(request)

    >>> response.status
    404

    >>> from pprint import pprint

    >>> pprint(response.headers)
    {'Accept-Ranges': ['bytes'],
    'Cache-Control': ['max-age=0, must-revalidate'],
    'Content-Type': ['text/html; charset=UTF-8'],
    'Date': ['Thu, 08 Dec 2016 16:21:19 GMT'],
    'Server': ['snooserv'],
    'Set-Cookie': ['loid=KqNLou0V9SKMX4qb4n; Domain=reddit.com; Max-Age=63071999; Path=/; expires=Sat, 08-Dec-2018 16:21:19 GMT; secure',
                    'loidcreated=2016-12-08T16%3A21%3A19.445Z; Domain=reddit.com; Max-Age=63071999; Path=/; expires=Sat, 08-Dec-2018 16:21:19 GMT; secure',
                    'loid=vi0ZVe4NkxNWdlH7r7; Domain=reddit.com; Max-Age=63071999; Path=/; expires=Sat, 08-Dec-2018 16:21:19 GMT; secure',
                    'loidcreated=2016-12-08T16%3A21%3A19.459Z; Domain=reddit.com; Max-Age=63071999; Path=/; expires=Sat, 08-Dec-2018 16:21:19 GMT; secure'],
    'Vary': ['accept-encoding'],
    'Via': ['1.1 varnish'],
    'X-Cache': ['MISS'],
    'X-Cache-Hits': ['0'],
    'X-Content-Type-Options': ['nosniff'],
    'X-Frame-Options': ['SAMEORIGIN'],
    'X-Moose': ['majestic'],
    'X-Served-By': ['cache-cdg8730-CDG'],
    'X-Timer': ['S1481214079.394283,VS0,VE159'],
    'X-Ua-Compatible': ['IE=edge'],
    'X-Xss-Protection': ['1; mode=block']}

Invoking the shell from spiders to inspect responses

Sometimes you want to inspect the responses that are being processed in a certain point of your spider, if only to check that response you expect is getting there.

This can be achieved by using the scrapy.shell.inspect_response function.

Here's an example of how you would call it from your spider:

System Message: WARNING/2 (<stdin>, line 253)

Cannot analyze code. Pygments package not found.

.. code-block:: python

    import scrapy


    class MySpider(scrapy.Spider):
        name = "myspider"
        start_urls = [
            "http://example.com",
            "http://example.org",
            "http://example.net",
        ]

        def parse(self, response):
            # We want to inspect one specific response.
            if ".org" in response.url:
                from scrapy.shell import inspect_response

                inspect_response(response, self)

            # Rest of parsing code.

When you run the spider, you will get something similar to this:

2014-01-23 17:48:31-0400 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://example.com> (referer: None)
2014-01-23 17:48:31-0400 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://example.org> (referer: None)
[s] Available Scrapy objects:
[s]   crawler    <scrapy.crawler.Crawler object at 0x1e16b50>
...

>>> response.url
'http://example.org'

Then, you can check if the extraction code is working:

System Message: WARNING/2 (<stdin>, line 290)

Cannot analyze code. Pygments package not found.

.. code-block:: pycon

    >>> response.xpath('//h1[@class="fn"]')
    []

Nope, it doesn't. So you can open the response in your web browser and see if it's the response you were expecting:

System Message: WARNING/2 (<stdin>, line 298)

Cannot analyze code. Pygments package not found.

.. code-block:: pycon

    >>> view(response)
    True

Finally you hit Ctrl-D (or Ctrl-Z in Windows) to exit the shell and resume the crawling:

>>> ^D
2014-01-23 17:50:03-0400 [scrapy.core.engine] DEBUG: Crawled (200) <GET http://example.net> (referer: None)
...

Note that you can't use the fetch shortcut here since the Scrapy engine is blocked by the shell. However, after you leave the shell, the spider will continue crawling where it stopped, as shown above.

</html>