Scraper2

Streamlined web crawler for rental listings

What it does

The scraper2 directory defines a generalized Craigslist rental listing crawler, and scripts like test_scraper.py and scrape_prior_day.py instantiate it with particular lists of search domains, time parameters, and other settings.

Functionality is similar to ClistRentScraper (developed by Geoff in 2014), but the operations are now defined explicitly rather than as Scrapy projects. This should make the crawler easier to maintain and debug. We use the Requests library for HTTP requests and Lxml to parse webpage content.

The crawler begins by loading a page of Craigslist search results, for example http://sfbay.craigslist.org/search/apa. From that page, it parses each listing's title, url, price, characteristics, and timestamp. Next, it visits each listing url to extract addresses and lat-lon coordinates. Then it moves on to the next page of search results and repeats the process.

The data is saved to a CSV file, and diagnostics and errors are saved to a log file.

ClistRentScraper only kept lat-lon coordinates, but Craigslist listings now also include a location accuracy indicator and an address or cross streets, when users have provided it. Scraper2 saves this data for future analysis.

Status

This project is on hold while we look into more official access to Craigslist data.

Task list (higher priority)

• Figure out what Craigslist's throttle thresholds are, and put rate limits into our scripts. On 5/6 they blocked my IP after requesting about 10,000 URLs over a few hours.

• Add a filter to avoid requesting URLs for listings that we know from the results page are missing necessary variables like price or number of bedrooms.

• Add docstrings and other proper code templating.

• Deploy on Linux server.

• Add option to upload data to S3.

• Add Slack status notification.

• Write unit tests.

• Craigslist returns a maximum of 2500 search results per query, which in high-traffic regions is much less than a full day of listings. For example, it's approx 6 daytime hours in the "sfbay" region. Here are some options: (a) run the scraper once a day at midnight and accept that we are getting an incomplete sample (current approach), (b) run the scraper more frequently, (c) try switching to sub-region searches.

Task list (lower priority)

• Improve log messages.

• Improve and test the fail conditions to make sure we won't get into recursive loops, and exit quickly when Craigslist throttles our requests.

• Is the list of data fields we're collecting optimal?

• Check the master list of Craigslist domains that we're crawling, which was compiled by Geoff in 2014. Is there a way to assemble the list programmatically, to make sure it's always up to date?

• Should we put the rental listings directly into a database as well as flat files?

• Develop a separate set of scripts for data cleaning, for example to remove duplicate listings.