🕷 SEO Crawling & Scraping: Strategies & Recipes

Once you have mastered the basics of using the crawl function, you probably want to achieve more with better customization and control.

These are some code strategies that might be useful to customize how you run your crawls.

Most of these options can be set using the custom_settings parameter that the function takes. This can be set by using a dictionary, where the keys indicate the option you want to set, and the values specify how you want to set them.

How to crawl a list of pages, and those pages only (list mode)?

Simply provide that list as the first argument, for the url_list parameter, and make sure that follow_links=False, which is the default. This simply crawls the given pages, and stops when done.

>>> import advertools as adv
>>> url_list = ['https://example.com/page_1',
...             'https://example.com/page_2',
...             'https://example.com/page_3',
...             'https://example.com/page_4']

>>> adv.crawl(url_list,
...           output_file='example_crawl_1.jl',
...           follow_links=False)

How can I crawl a website including its sub-domains?

The crawl function takes an optional allowed_domains parameter. If not provided, it defaults to the domains of the URLs in url_list. When the crawler goes through the pages of example.com, it follows links to discover pages. If it finds pages on help.exmaple.com it won’t crawl them (it’s a different domain). The solution, therefore, is to provide a list of domains to the allowed_domains parameter. Make sure you also include the original domain, in this case example.com.

>>> adv.crawl('https://example.com',
...           'example_crawl_1.jl',
...           follow_links=True
...           allowed_domains=['help.example.com', 'example.com', 'community.example.com'])

How can I save a copy of the logs of my crawl for auditing them later?

It’s usually good to keep a copy of the logs of all your crawls to check for errors, exceptions, stats, etc. Pass a path of the file where you want the logs to be saved, in a dictionary to the cutom_settings parameter. A good practice for consistency is to give the same name to the output_file and log file (with a different extension) for easier retreival. For example:

output_file: ‘website_name_crawl_1.jl’
LOG_FILE: ‘website_name_crawl_1.log’ (.txt can also work)
output_file: ‘website_name_crawl_2.jl’
LOG_FILE: ‘website_name_crawl_2.log’
>>> adv.crawl('https://example.com', 'example_crawl_1.jl',
...           custom_settings={'LOG_FILE': 'example_crawl_1.log'})

How can I automatically stop my crawl based on a certain condition?

There are a few conditions that you can use to trigger the crawl to stop, and they mostly have descriptive names:

  • CLOSESPIDER_ERRORCOUNT: You don’t want to wait three hours for a crawl to finish, only to discover that you had errors all over the place. Set a certain number of errors to trigger the crawler to stop, so you can investigate the issue.

  • CLOSESPIDER_ITEMCOUNT: Anything scraped from a page is an “item”, h1, title , meta_desc, etc. Set the crawler to stop after getting a certain number of items if you want that.

  • CLOSESPIDER_PAGECOUNT: Stop the crawler after a certain number of pages have been crawled. This is useful as an exploratory technique, especially with very large websites. It might be good to crawl a few thousand pages, get an idea on its structure, and then run a full crawl with those insights in mind.

  • CLOSESPIDER_TIMEOUT: Stop the crawler after a certain number of seconds.

>>> adv.crawl('https://example.com', 'example_crawl_1.jl',
...           custom_settings={'CLOSESPIDER_PAGECOUNT': 500})

How can I (dis)obey robots.txt rules?

The crawler obeys robots.txt rules by default. Sometimes you might want to check the results of crawls without doing that. You can set the ROBOTSTXT_OBEY setting under custom_settings:

>>> adv.crawl('https://example.com',
...           'example_crawl_1.jl',
...           custom_settings={'ROBOTSTXT_OBEY': False})

How do I set my User-agent while crawling?

Set this parameter under custom_settings dictionary under the key USER_AGENT. The default User-agent can be found by running adv.spider.user_agent

>>> adv.spider.user_agent # to get the current User-agent
>>> adv.crawl('http://example.com',
...           'example_crawl_1.jl',
...           custom_settings={'USER_AGENT': 'YOUR_USER_AGENT'})

How can I control the number of concurrent requests while crawling?

Some servers are set for high sensitivity to automated and/or concurrent requests, that you can quickly be blocked/banned. You also want to be polite and not kill those servers, don’t you?

There are several ways to set that under the custom_settings parameter. The available keys are the following:

CONCURRENT_ITEMS: default 100
CONCURRENT_REQUESTS : default 16
CONCURRENT_REQUESTS_PER_DOMAIN: default 8
CONCURRENT_REQUESTS_PER_IP: default 0
>>> adv.crawl('https://example.com',
...           'example_crawl_1.jl',
...           custom_settings={'CONCURRENT_REQUESTS_PER_DOMAIN': 1})

How can I slow down the crawling so I don’t hit the websites’ servers too hard?

Use the DOWNLOAD_DELAY setting and set the interval to be waited before downloading consecutive pages from the same website (in seconds).

>>> adv.crawl('https://example.com', 'example_crawl_1.jl',
...           custom_settings={'DOWNLOAD_DELAY': 3}) # wait 3 seconds between pages

How can I set multiple settings to the same crawl job?

Simply add multiple settings to the custom_settings parameter.

>>> adv.crawl('http://example.com',
...           'example_crawl_1.jl',
...           custom_settings={'CLOSESPIDER_PAGECOUNT': 400,
...                            'CONCURRENT_ITEMS': 75,
...                            'LOG_FILE': 'output_file.log'})

How do I pause/resume crawling, while making sure I don’t crawl the same page twice?

There are several reasons why you might want to do this:

  • You want to mainly crawl the updates to the site (you already crawled the site).

  • The site is very big, and can’t be crawled quickly.

  • You are not in a hurry, and you also don’t want to hit the servers hard, so you run your crawl across days for example.

  • As an emergency measure (connection lost, battery died, etc.) you can start where you left off

Handling this is extremely simple, and all you have to do is simply provide a path to a new folder. Make sure it is new and empty, and make sure to only use it for the same crawl job reruns. That’s all you have to worry about. The JOBDIR setting handles this.

>>> adv.crawl('http://example.com',
...           'example_crawl_1.jl',
...           custom_settings={'JOBDIR': '/Path/to/en/empty/folder'})

The first time you run the above code and then stop it. Stopping can happen by accident (lost connection, closed computer, etc.), manually (you hit ctrl+C) or you used a custom setting option to stop the crawl after a certain number of pages, seconds, etc.

The second time you want to run this, you simply run the exact same command again. If you check the folder that was created you can see a few files that manage the process. You don’t need to worry about any of it. But make sure that folder doesn’t get changed manually, rerun the same command as many times as you need, and the crawler should handle de-duplication for you.