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Robots Exclusion Protocol Parser for Python

Build Status

This started out of a lack of memoization support in other robots.txt parsers I've encountered, and the lack of support for Crawl-delay and Sitemap in the built-in robotparser.

Features

  • Configurable caching of robots.txt files
  • Expiration based on the Expires and Cache-Control headers
  • Configurable automatic refetching basing on expiration
  • Support for Crawl-delay
  • Support for Sitemaps
  • Wildcard matching

Matching

This package supports the 1996 RFC, as well as additional commonly-implemented features, like wildcard matching, crawl-delay, and sitemaps. There are varying approaches to matching Allow and Disallow. One approach is to use the longest match. Another is to use the most specific. This package chooses to follow the directive that is longest, the assumption being that it's the one that is most specific -- a term that is a little difficult to define in this context.

Usage

The easiest way to use reppy, you first need a cache object. This object controls how fetched robots.txt are stored and cached, and provides an interface to issue queries about urls.

from reppy.cache import RobotsCache
# Any args and kwargs provided here are given to `requests.get`. You can use
# this to set request headers and the like
robots = RobotsCache()
# Now ask if a particular url is allowed
robots.allowed('http://example.com/hello', 'my-agent')

By default, it fetches robots.txt for you using requests. If you're, interested in getting a Rules object (which is a parsed robots.txt file), you can ask for it without it being cached:

# This returns a Rules object, which is not cached, but can answer queries
rules = robots.fetch('http://example.com/')
rules.allowed('http://example.com/foo', 'my-agent')

If automatic fetching doesn't suit your needs (perhaps you have your own way of fetching pages), you can still make use of the cache object. To do this, you'll need to make your own Rules object:

from reppy.parser import Rules
# Do some fetching here
# ...
robots.add(Rules('http://example.com/robots.txt',
	status_code,     # What status code did we get back?
	content,         # The content of the fetched page
	expiration))     # When is this page set to expire?

Expiration

A RobotsCache object can track the expiration times for fetched robots.txt files. This is taken from either the Cache-Control or Expires headers if they are present, or defaults to an hour. At some point, I would like this to be configurable, but I'm still trying to think of the best interface.

rules = RobotsCache.find('http://example.com/robots.txt')
# Now long before it expires?
rules.ttl
# When does it expire?
rules.expires
# Has it expired?
rules.expired

Caching

The default caching policy is to cache everything until it expires. At some point, we'll add other caching policies (probably LRU), but you can also extend the RobotsCache object to implement your own. Override the cache method and you're on your way!

class MyCache(RobotsCache):
	def cache(self, url, *args, **kwargs):
	    fetched = self.fetch(url, *args, **kwargs)
	    self._cache[Utility.hostname(url)] = fetched
	    # Figure out any cached items that need eviction
	    return fetched

You may want to explicitly clear the cache, too, which can be done either with the clear method, or it's done automatically when used as a context manager:

# Store some results
robots.allowed('http://example.com/foo')
# Now we'll get rid of the cache
robots.clear()

# Now as a context manager
with robots:
	robots.allowed('http://example.com/foo')

# Now there's nothing cached in robots

Queries

Allowed / Disallowed

Each of these takes a url and a short user agent string (for example, 'my-agent').

robots.allowed('http://example.com/allowed.html', 'my-agent')
# True
robots.disallowed('http://example.com/allowed.html', 'my-agent')
# False

Alternatively, a rules object provides the same interface:

rules = robots.find('http://example.com/allowed')
rules.allowed('http://example.com/allowed', 'my-agent')

Crawl-Delay

Crawl delay can be specified on a per-agent basis, so when checking the crawl delay for a site, you must provide an agent.

robots.delay('http://example.com/foo', 'my-agent')

If there is no crawl delay specified for the provided agent /or/ for the * agent, then delay returns None

Sitemaps

A robots.txt file can also specify sitemaps, accessible through a Rules object or a RobotsCache object:

robots.sitemaps('http://example.com/')

Path-Matching

Path matching supports both * and $

Running Tests

In order to run tests, you'll need nose, asis, gevent and coverage, all of which can be installed with pip:

sudo pip install -r dev-requirements.txt

From there, the tests may be run with:

make test