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User guide

reader

This page gives a tour of reader's features, and a few examples of how to use them.

Note

Before starting, make sure that reader is installed <install> and up-to-date.

The Reader object

The Reader object persists feed and entry state and provides operations on them.

To create a new Reader, call make_reader with the path to a database file:

>>> from reader import make_reader
>>> reader = make_reader("db.sqlite")

The default (and currently only) storage uses SQLite, so the path behaves like the database argument of sqlite3.connect:

  • If the database does not exist, it will be created automatically.
  • You can pass ":memory:" to use a temporary in-memory database; the data will disappear when the reader is closed.

After you are done with the reader, call ~Reader.close() to release the resources associated with it:

>>> reader.close()

While the same thing will eventually happen when the reader is garbage-collected, it is recommended to call ~Reader.close() explicitly, especially in long-running processes or when you create multiple readers pointing to the same database. You can use contextlib.closing to do this automatically:

>>> from contextlib import closing
>>> with closing(make_reader('db.sqlite')) as reader:
...     ... # do stuff with reader
...

File-system access

reader supports http(s):// and local (file:) feeds.

For security reasons, you might want to restrict file-system access to a single directory or prevent it entirely; you can do so by using the feed_root make_reader argument:

>>> # local feed paths are relative to /feeds
>>> reader = make_reader("db.sqlite", feed_root='/feeds')
>>> # ok, resolves to /feeds/feed.xml
>>> reader.add_feed("feed.xml")
>>> # ok, resolves to /feeds/also/feed.xml
>>> reader.add_feed("file:also/feed.xml")
>>> # error on update, resolves to /feed.xml, which is above /feeds
>>> reader.add_feed("file:../feed.xml")
>>> # all local paths will fail to update
>>> reader = make_reader("db.sqlite", feed_root=None)

Note that it is still possible to add local feeds regardless of feed_root; it is updating them that will fail.

Adding feeds

To add a feed, call the ~Reader.add_feed method with the feed URL:

>>> reader.add_feed("https://www.relay.fm/cortex/feed")
>>> reader.add_feed("http://www.hellointernet.fm/podcast?format=rss")

Most of the attributes of a new feed are empty (to populate them, the feed must be updated):

>>> feed = reader.get_feed("http://www.hellointernet.fm/podcast?format=rss")
>>> print(feed)
Feed(url='http://www.hellointernet.fm/podcast?format=rss', updated=None, title=None, ...)

Deleting feeds

To delete a feed and all the data associated with it, use ~Reader.remove_feed:

>>> reader.remove_feed("https://www.example.com/feed.xml")

Updating feeds

To retrieve the latest version of a feed, along with any new entries, it must be updated. You can update all the feeds by using the ~Reader.update_feeds method:

>>> reader.update_feeds()
>>> reader.get_feed(feed)
Feed(url='http://www.hellointernet.fm/podcast?format=rss', updated=datetime.datetime(2020, 2, 28, 9, 34, 2), title='Hello Internet', ...)

To retrive feeds in parallel, use the workers flag:

>>> reader.update_feeds(workers=10)

You can also update a specific feed using ~Reader.update_feed:

>>> reader.update_feed("http://www.hellointernet.fm/podcast?format=rss")

If supported by the server, reader uses the ETag and Last-Modified headers to only retrieve feeds if they changed (details). Even so, you should not update feeds too often, to avoid wasting the feed publisher's resources, and potentially getting banned; every 30 minutes seems reasonable.

To support updating newly-added feeds off the regular update schedule, you can use the new_only flag; you can call this more often (e.g. every minute):

>>> reader.update_feeds(new_only=True)

Disabling feed updates

Sometimes, it is useful to skip a feed when using ~Reader.update_feeds; for example, the feed does not exist anymore, and you want to stop requesting it unnecessarily during regular updates, but still want to keep its entries (so you cannot remove it).

~Reader.disable_feed_updates allows you to do exactly that:

>>> reader.disable_feed_updates(feed)

You can check if updates are enabled for a feed by looking at its ~Feed.updates_enabled attribute:

>>> reader.get_feed(feed).updates_enabled
False

Getting feeds

As seen in the previous sections, ~Reader.get_feed returns a Feed object with more information about a feed:

>>> from prettyprinter import pprint, install_extras;
>>> install_extras(include=['dataclasses'])
>>> feed = reader.get_feed(feed)
>>> pprint(feed)
reader.types.Feed(
    url='http://www.hellointernet.fm/podcast?format=rss',
    updated=datetime.datetime(
        year=2020,
        month=2,
        day=28,
        hour=9,
        minute=34,
        second=2
    ),
    title='Hello Internet',
    link='http://www.hellointernet.fm/',
    author='CGP Grey',
    added=datetime.datetime(2020, 10, 12),
    last_updated=datetime.datetime(2020, 10, 12)
)

To get all the feeds, use the ~Reader.get_feeds method:

>>> for feed in reader.get_feeds():
...     print(
...         feed.title or feed.url,
...         f"by {feed.author or 'unknown author'},",
...         f"updated on {feed.updated or 'never'}",
...     )
...
Cortex by Relay FM, updated on 2020-09-14 12:15:00
Hello Internet by CGP Grey, updated on 2020-02-28 09:34:02

~Reader.get_feeds also allows filtering feeds by their tags, if the last update succeeded, or if updates are enabled, and changing the feed sort order.

Changing feed URLs

Sometimes, feeds move from one URL to another.

This can be handled naively by removing the old feed and adding the new URL; however, all the data associated with the old feed would get lost, including any old entries (some feeds only have the last X entries).

To change the URL of a feed in-place, use ~Reader.change_feed_url:

>>> reader.change_feed_url(
...     "https://www.example.com/old.xml",
...     "https://www.example.com/new.xml"
... )

Sometimes, the id of the entries changes as well; you can handle duplicate entries by using a plugin <plugins> like feed_entry_dedupe.

Getting entries

You can get all the entries, most-recent first, by using ~Reader.get_entries(), which generates Entry objects:

>>> for entry, _ in zip(reader.get_entries(), range(10)):
...     print(entry.feed.title, '-', entry.title)
...
Cortex - 106: Clear and Boring
...
Hello Internet - H.I. #136: Dog Bingo

~Reader.get_entries allows filtering entries by their feed, flags, feed tags, or enclosures, and changing the entry sort order. Here is an example of getting entries for a single feed:

>>> feed.title
'Hello Internet'
>>> entries = list(reader.get_entries(feed=feed))
>>> for entry in entries[:2]:
...     print(entry.feed.title, '-', entry.title)
...
Hello Internet - H.I. #136: Dog Bingo
Hello Internet - H.I. #135: Place Your Bets

Entry flags

Entries can be marked as read <Reader.mark_as_read> or as important <Reader.mark_as_important>.

These flags can be used for filtering:

>>> reader.mark_as_read(entries[0])
>>> entries = list(reader.get_entries(feed=feed, read=False))
>>> for entry in entries[:2]:
...     print(entry.feed.title, '-', entry.title)
...
Hello Internet - H.I. #135: Place Your Bets
Hello Internet - # H.I. 134: Boxing Day

Full-text search

Note

The search functionality is optional, use the search extra to install its dependencies <Optional dependencies>.

reader supports full-text searches over the entries' content through the ~Reader.search_entries() method.

Since search adds some overhead, it needs to be enabled by calling ~Reader.enable_search() (this is persistent across Reader instances using the same database, and only needs to be done once). Also, the search index must be kept in sync by calling ~Reader.update_search() regularly (usually after updating the feeds).

>>> reader.enable_search()
>>> reader.update_search()
>>> for result in reader.search_entries('mars'):
...     print(result.metadata['.title'].apply('*', '*'))
...
H.I. #106: Water on *Mars*

~Reader.search_entries() generates EntrySearchResult objects, which contain snippets of relevant entry/feed fields, with the parts that matched highlighted.

Talk about how you can eval() on an entry to get the corresponding field.

By default, the results are filtered by relevance; you can sort them most-recent first by passing sort='recent'.

~Reader.search_entries() allows filtering the results just as ~Reader.get_entries() does.

Feed metadata

Feeds can have metadata, key-value pairs where the values are any JSON-serializable data:

>>> reader.get_feed_metadata(feed, 'key', 'default')
'default'
>>> reader.set_feed_metadata(feed, 'key', 'value')
>>> reader.get_feed_metadata(feed, 'key', 'default')
'value'
>>> reader.set_feed_metadata(feed, 'another', {'one': [2]})
>>> dict(reader.iter_feed_metadata(feed))
{'another': {'one': [2]}, 'key': 'value'}

Common uses for metadata are plugin and UI settings.

Mention reader doesn't restrict key characters, but the UI should.

Mention reserved key prefixes (186).

Feed tags

Feeds can also have tags:

>>> reader.add_feed_tag(feed, 'one')
>>> reader.add_feed_tag(feed, 'two')
>>> set(reader.get_feed_tags(feed))
{'one', 'two'}

Tags can be used for filtering feeds and entries (see the ~Reader.get_feeds() documentation for more complex examples):

>>> # feeds that have the tag "one"
>>> [f.title for f in reader.get_feeds(tags=['one'])]
['Hello Internet']
>>> # entries of feeds that have no tags
>>> [
...     (e.feed.title, e.title)
...     for e in reader.get_entries(feed_tags=[False])
... ][:2]
[('Cortex', '106: Clear and Boring'), ('Cortex', '105: Atomic Notes')]

Mention reader doesn't restrict tag characters, but the UI should.

Mention reserved tag prefixes (186).

Counting things

You can get aggregated feed and entry counts by using one of the ~Reader.get_feed_counts, ~Reader.get_entry_counts, or ~Reader.search_entry_counts methods:

>>> reader.get_feed_counts()
FeedCounts(total=134, broken=3, updates_enabled=132)
>>> reader.get_entry_counts()
EntryCounts(total=11843, read=9762, important=45, has_enclosures=4273)
>>> reader.search_entry_counts('hello internet')
EntrySearchCounts(total=207, read=196, important=0, has_enclosures=172)

The _counts methods support the same filtering arguments as their non-_counts counterparts. The following example shows how to get counts only for feeds/entries with a specific tag:

>>> for tag in chain(reader.get_feed_tags(), [False]):
...     feeds = reader.get_feed_counts(tags=[tag])
...     entries = reader.get_entry_counts(feed_tags=[tag])
...     print(f"{tag or '<no tag>'}: {feeds.total} feeds, {entries.total} entries ")
...
podcast: 29 feeds, 4277 entries
python: 29 feeds, 1281 entries
self: 2 feeds, 67 entries
tech: 79 feeds, 5527 entries
webcomic: 6 feeds, 1609 entries
<no tag>: 22 feeds, 1118 entries

Feed and entry arguments

As you may have noticed in the examples above, feed URLs and Feed objects can be used interchangeably as method arguments. This is by design. Likewise, wherever an entry argument is expected, you can either pass a (feed URL, entry id) tuple or an Entry (or EntrySearchResult) object.

Streaming methods

All methods that return iterators (~Reader.get_feeds(), ~Reader.get_entries() etc.) generate the results lazily.

Some examples of how this is useful:

  • Consuming the first 100 entries should take roughly the same amount of time, whether you have 1000 or 100000 entries.
  • Likewise, if you don't keep the entries around (e.g. append them to a list), memory usage should remain relatively constant regardless of the total number of entries returned.

Advanced feedparser features

reader uses feedparser ("Universal Feed Parser") to parse feeds. It comes with a number of advanced features, most of which reader uses transparently.

Two of these features are worth mentioning separately, since they change the content of the feed, and, although always enabled at the moment, they may become optional in the future; note that disabling them is not currently possible.

Sanitization

Quoting:

Most feeds embed HTML markup within feed elements. Some feeds even embed other types of markup, such as SVG or MathML. Since many feed aggregators use a web browser (or browser component) to display content, Universal Feed Parser sanitizes embedded markup to remove things that could pose security risks.

You can find more details about which markup and elements are sanitized in the feedparser documentation.

The following corresponding reader attributes are sanitized:

  • Entry.content (Content.value)
  • Entry.summary
  • Entry.title
  • Feed.title

Relative link resolution

Quoting:

Many feed elements and attributes are URIs. Universal Feed Parser resolves relative URIs according to the XML:Base specification. [...]

In addition [to elements treated as URIs], several feed elements may contain HTML or XHTML markup. Certain elements and attributes in HTML can be relative URIs, and Universal Feed Parser will resolve these URIs according to the same rules as the feed elements listed above.

You can find more details about which elements are treated as URIs and HTML markup in the feedparser documentation.

The following corresponding reader attributes are treated as URIs:

  • Entry.enclosures (Enclosure.href)
  • Entry.id
  • Entry.link
  • Feed.link

The following corresponding reader attributes may be treated as HTML markup, depending on their type attribute or feedparser defaults:

  • Entry.content (Content.value)
  • Entry.summary
  • Entry.title
  • Feed.title

Errors and exceptions

All exceptions that Reader explicitly raises inherit from ReaderError.

If there's an issue retrieving or parsing the feed, ~Reader.update_feed will raise a ParseError with the original exception (if any) as cause. ~Reader.update_feeds will just log the exception and move on. In both cases, information about the cause will be stored on the feed in ~Feed.last_exception.

Any unexpected exception raised by the underlying storage implementation will be reraised as a StorageError, with the original exception as cause.

Search methods will raise a SearchError. Any unexpected exception raised by the underlying search implementation will be also be reraised as a SearchError, with the original exception as cause.

When trying to create a feed, entry, metadata that already exists, or to operate on one that does not exist, a corresponding *ExistsError or *NotFoundError will be raised.

feed operations (remove, filtering, user title) get_feeds() vs get_feed() (same for entry)