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Wikipedia API returning an empty string for text extract on some articles
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Description

In the last week or so I've noticed that the Wikipedia API has started returning an empty string when querying for text extracts from certain articles, such as this query about the Cosmic Anisotropy Telescope: https://en.wikipedia.org/w/api.php?action=query&format=json&prop=extracts&titles=Cosmic%20Anisotropy%20Telescope&exsentences=10&explaintext=1&exlimit=1

Casting around for a few others - 1, 2, 3, 4 - I can't see any obvious pattern in why these particular ones would return blank. (The same query works fine on most articles, eg. this.)

Is this a bug, or has there been an update to the API that's caused the query I normally use to behave differently? I've been using this kind of query for months and it's only recently started returning blank strings.

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LordBelbury created this task.Sep 7 2018, 12:09 PM
Restricted Application added a subscriber: Aklapper. · View Herald TranscriptSep 7 2018, 12:09 PM
Anomie subscribed.Sep 7 2018, 1:11 PM

Try purging the pages with the problem. It may be due to a recent change to how parser output is handled.

Anomie moved this task from Unsorted to Non-core-API stuff on the MediaWiki-Action-API board.Sep 7 2018, 1:11 PM
LordBelbury added a comment.Sep 7 2018, 1:15 PM

Thanks, that seems to be it. I tried a purge on the first two listed above and it fixed the problem.

Will all the (presumably thousands) of other affected articles purge themselves automatically, given time?

Anomie added a comment.Sep 7 2018, 2:07 PM

The parser cache entries will expire over the next month. The change in https://gerrit.wikimedia.org/r/c/mediawiki/core/+/458732 would fix the interpretation of those old entries before they expire.

Aklapper mentioned this in T203744: TextExtracts gives empty extract for many pages.Sep 7 2018, 2:22 PM
Aklapper merged a task: T203744: TextExtracts gives empty extract for many pages.
Aklapper added a project: TextExtracts.
Aklapper added subscribers: Kainedadev, Agold10, Frettie.
Agold10 added a comment.Sep 7 2018, 2:57 PM

How can I purge a page, please?

Jdlrobson added a project: Web-Team-Backlog (Tracking).EditedSep 7 2018, 3:00 PM
Jdlrobson subscribed.
In T203785#4566540, @Agold10 wrote:

How can I purge a page, please?

Apply action=purge to the url
e.g. https://en.wikipedia.org/wiki/London?action=purge

Anomie closed this task as Resolved.Sep 10 2018, 2:32 PM
Anomie assigned this task to Tgr.

This should be fixed now with the backport of rMW392446738756: Unwrap HTML loaded from parser cache.

Jdlrobson awarded a token.Sep 10 2018, 5:55 PM
Aklapper removed a subscriber: Anomie.Oct 16 2020, 5:38 PM
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