ampelopsis is a simple crawler, recursively downloading pages from specified hosts. It doesn't do much with the downloaded pages beyond storing, optionally compressing and indexing them (in a PostgreSQL database) - it's designed to be a step in a larger, more useful pipeline, modular and easily extensible. Its code is in scripts in the python source directory. ampelopsis is written in Python 3, and in addition to psycopg2, it requires PycURL (for parallelized download) and lxml (for HTML parsing).
Before running ampelopsis, it's necessary to create its database, also named ampelopsis, by running the scripts in sql source directory. Database access must be specified in an ampelopsis.ini configuration file, placed in the top directory (above the python and sql directories):
[root] dbuser = name dbpass = password
Other configuration settings are optional; some are mentioned below. After configuration, the crawler is ready to run, except it doesn't yet know what to crawl. That is specified in the ampelopsis database tables, and the easiest way to initialize them is by running the seed.py script with the top-level URLs (or hostnames) on its command line. The crawler follows links only to hostnames passed to seed.py (or, less strictly, to their domains, when the match_domain option is set).
Default downloader is in the download.py script - when run, it downloads the top-level URLs and waits for more work. More work is normally provided by the parse.py script, which parses the downloaded pages and stores links in them (that have the whitelisted domains) to the database. Downloader and parser can be run at the same time, and multiple times in parallel, which isn't particularly useful for the default setup (download.py multiplexes connections internally, up to the value of max_num_conn setting, and parse.py is generally fast enough to keep up with download), but becomes handy when using drive.py (see doc/js.md).
The 'master' branch contains just one parser, but it's expected that specific scraping projects will modify or replace it, e.g. to be more selective in which URLs it feeds back to downloader (see the 'cro' branch for a more advanced example). Using the unmodified parse.py, found links can be filtered by specifying url_whitelist_rx or url_blacklist_rx setting. Downloader and parser communicate through the database, using PostgreSQL notifications.
Some other notes are available in the doc directory. For more detail, use the source.