User guide¶
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 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 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 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 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 delete_feed()
:
>>> reader.delete_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 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 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)
If you need the status of each feed as it gets updated
(for instance, to update a progress bar),
you can use update_feeds_iter()
instead,
and get a (url, updated feed or none or exception) pair for each feed:
>>> for url, value in reader.update_feeds_iter():
... if value is None:
... print(url, "not modified")
... elif isinstance(value, Exception):
... print(url, "error:", value)
... else:
... print(url, value.new, "new,", value.updated, "updated")
...
http://www.hellointernet.fm/podcast?format=rss 100 new, 0 updated
https://www.relay.fm/cortex/feed not modified
Disabling feed updates¶
Sometimes, it is useful to skip a feed when using 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).
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
updates_enabled
attribute:
>>> reader.get_feed(feed).updates_enabled
False
Getting feeds¶
As seen in the previous sections,
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 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
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 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
like feed_entry_dedupe
.
Getting entries¶
You can get all the entries, most-recent first,
by using 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
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
or as important
.
These flags can be used for filtering:
>>> reader.mark_entry_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.
reader supports full-text searches over the entries’ content through the search_entries()
method.
Since search adds some overhead,
it needs to be enabled by calling 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
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*
search_entries()
generates EntrySearchResult
objects,
which contain snippets of relevant entry/feed fields,
with the parts that matched highlighted.
By default, the results are filtered by relevance;
you can sort them most-recent first by passing sort='recent'
.
search_entries()
allows filtering the results just as get_entries()
does.
Feed metadata¶
Feeds can have metadata, key-value pairs where the values are any JSON-serializable data:
>>> reader.get_feed_metadata_item(feed, 'key', 'default')
'default'
>>> reader.set_feed_metadata_item(feed, 'key', 'value')
>>> reader.get_feed_metadata_item(feed, 'key', 'default')
'value'
>>> reader.set_feed_metadata_item(feed, 'another', {'one': [2]})
>>> dict(reader.get_feed_metadata(feed))
{'another': {'one': [2]}, 'key': 'value'}
Common uses for metadata are plugin and UI settings.
Note that metadata keys and the top-level keys of dict metadata values starting with specific (configurable) prefixes are reserved. Other than that, they can be any unicode string, although UIs might want to restrict this to a smaller character set.
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 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')]
Note that tags starting with specific (configurable) prefixes are reserved. Other than that, they can be any unicode string, although UIs might want to restrict this to a smaller character set.
Counting things¶
You can get aggregated feed and entry counts by using one of the
get_feed_counts()
,
get_entry_counts()
, or
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
Pagination¶
get_feeds()
, get_entries()
,
and search_entries()
can be used in a paginated fashion.
The limit
argument allows limiting the number of results returned;
the starting_after
argument allows skipping results until after
a specific one.
To get the first page, use only limit
:
>>> for entry in reader.get_entries(limit=2):
... print(entry.title)
...
H.I. #136: Dog Bingo
H.I. #135: Place Your Bets
To get the next page, use the last result from a call as
starting_after
in the next call:
>>> for entry in reader.get_entries(limit=2, starting_after=entry):
... print(entry.title)
...
# H.I. 134: Boxing Day
Star Wars: The Rise of Skywalker, Hello Internet Christmas Special
Plugins¶
reader supports plugins as a way to extend its default behavior.
To use a built-in plugin, pass the plugin name to make_reader()
:
>>> reader = make_reader("db.sqlite", plugins=[
... "reader.enclosure_dedupe",
... "reader.entry_dedupe",
... ])
You can find the full list of built-in plugins here.
By default, only reader.ua_fallback
is enabled.
Custom plugins¶
In addition to built-in plugins, reader also supports custom plugins.
A custom plugin is any callable that takes a Reader
instance
and potentially modifies it in some (useful) way.
To use custom plugins, pass them to make_reader()
:
>>> def function_plugin(reader):
... print(f"got {reader}")
...
>>> class ClassPlugin:
... def __init__(self, **options):
... self.options = options
... def __call__(self, reader):
... print(f"got options {self.options} and {reader}")
...
>>> reader = make_reader("db.sqlite", plugins=[
... function_plugin,
... ClassPlugin(option=1),
... ])
got <reader.core.Reader object at 0x7f8897824a00>
got options {'option': 1} and <reader.core.Reader object at 0x7f8897824a00>
For a real-world example, see the implementation of the enclosure_dedupe built-in plugin. Using it as a custom plugin looks like this:
>>> from reader.plugins import enclosure_dedupe
>>> reader = make_reader("db.sqlite", plugins=[enclosure_dedupe.init_reader])
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.
You can get this unique identifier in a uniform way by using the object_id
property.
This is useful when you need to refer to a reader object in a generic way
from outside Python (e.g. to make a link to the next page
of feeds/entries in a web application).
Streaming methods¶
All methods that return iterators
(get_feeds()
, 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.
Reserved names¶
In order to expose reader and plugin functionality directly to the end user,
names starting with .reader.
and .plugin.
are reserved.
This applies to the following names:
tags
metadata keys
the top-level keys of dict metadata values
Currently, there are no reader-reserved names; new ones will be documented here.
The prefixes can be changed using
reserved_name_scheme
.
Note that changing reserved_name_scheme
does not rename the actual entities,
it just controls how new reserved names are built.
Because of this, I recommend choosing a scheme
before setting up a new reader database,
and sticking with that scheme for its lifetime.
To change the scheme of an existing database,
you must rename the entities listed above yourself.
When choosing a reserved_name_scheme
,
the reader_prefix
and plugin_prefix
should not overlap,
otherwise the reader core and various plugins may interfere each other.
(For example, if both prefixes are set to .
,
reader-reserved key user_title
and a plugin named user_title
that uses just the plugin name (with no key)
will both end up using the .user_title
metadata.)
That said, reader will ensure names reserved by the core and built-in plugin names will never collide, so this is a concern only if you plan to use third-party plugins.
Reserved names can be built programmatically using
make_reader_reserved_name()
and make_plugin_reserved_name()
.
Code that wishes to work with any scheme
should always use these methods to construct reserved names
(especially third-party plugins).
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:
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:
The following corresponding reader attributes may be treated as HTML markup, depending on their type attribute or feedparser defaults:
Errors and exceptions¶
All exceptions that Reader
explicitly raises inherit from
ReaderError
.
If there’s an issue retrieving or parsing the feed,
update_feed()
will raise a ParseError
with the original exception (if any) as cause.
update_feeds()
will just log the exception and move on.
In both cases, information about the cause will be stored on the feed in
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.
All functions and methods may raise
ValueError
or TypeError
implicitly or explicitly
if passed invalid arguments.