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XML parsing problems
Posted: Fri Nov 06, 2009 1:31 pm
by hilti
Hi!
I'm trying to implement a simple RSS and ATOM reading function, but I got some problems in parsing this kind of elements
Example from NYTimes.com RSS feed
Code: Select all
<dc:creator>By ROBERT D. McFADDEN</dc:creator>
This one doesn't work
Code: Select all
; TODO: Problems in parsing media:content - ask the forum
;(lookup '(media:content @ url) item) "<br/>"
You can check out my current efforts on this page:
http://www.rundragonfly.com/dragonfly_feeds
Cheers!
Hilti
Re: XML parsing problems
Posted: Fri Nov 06, 2009 3:00 pm
by Lutz
the xml you posted is parsed like this:
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> (set 'xml "<dc:creator>By ROBERT D. McFADDEN</dc:creator>")
"<dc:creator>By ROBERT D. McFADDEN</dc:creator>"
> (xml-type-tags nil nil nil nil)
(nil nil nil nil)
> (set 'sxml (xml-parse xml 31))
((dc:creator "By ROBERT D. McFADDEN"))
> (lookup (sym "dc:creator") sxml) ; <- the correct way to do it
"By ROBERT D. McFADDEN"
>
you cannot say:
Code: Select all
(lookup 'dc:creator sxml) => nil ; <- wrong way
In the 'lookip' statement It takes 'dc' as a namespace qualifier because of the colon. Although 'xml-parse' created a symbol "dc:creator" with an illegal colon in it. Using (sym "dc:creator") you can still create that symbol and do the lookup.
you also could this:
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> (set 'creator (sym "dc:creator"))
dc:creator
> (lookup creator sxml)
"By ROBERT D. McFADDEN"
>
Re: XML parsing problems
Posted: Sat Nov 07, 2009 8:49 pm
by hilti
Thanks Lutz! Parsing for elements like
Code: Select all
<dc:creator>By ALISSA J. RUBIN</dc:creator>
is working great. See it here:
http://www.rundragonfly.com/dragonfly_feeds
But one thing I can't get working - the media elements, e.g. NYTimes.com RSS feed
Code: Select all
<media:content url="http://graphics8.nytimes.com/images/2009/11/08/world/08basra_CA0/thumbStandard.jpg" medium="image" height="75" width="75"/>
I don't know how to access the "url" and "medium" elements.
Thanks for help!
Hilti (slowly getting a RSS parsing expert ;-)
Re: XML parsing problems
Posted: Sat Nov 07, 2009 11:04 pm
by cormullion
If you can get as far as this:
Code: Select all
(set 'mc '(media:content
(@
(url "http://graphics8.nytimes.com/images/2009/11/08/world/08peru_CA0/thumbStandard.jpg")
(medium "image")
(height "75")
(width "75"))))
then
Code: Select all
(lookup 'url (rest (first (rest mc))))
will get
http://graphics8.nytimes.com/images/200 ... andard.jpg
Re: XML parsing problems
Posted: Sun Nov 08, 2009 12:58 pm
by Lutz
Another method uses the 'ref' function:
Code: Select all
(set 'mc '(media:content
(@
(url "http://graphics8.nytimes.com/images/.../thumbStandard.jpg")
(medium "image")
(height "75")
(width "75"))))
(last (mc (ref '(url *) mc match)))
;=> "http://graphics8.nytimes.com/.../thumbStandard.jpg"
The advantage here is, that 'ref' reaches into all nesting levels of a list. The above solution wouldn't need to change if the structure of the XML changes. As long as there is an (url *) elelement in it, 'ref' will find it.
'ref-all' is a version of 'ref' which returns all index vectors found, not only the first one:
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(set 'mc '(( x y z (url "A.com")) (q ( z (url "B.com"))) (url "C.com")))
(set 'vectors (ref-all '(url *) mc match)) ;=> ((0 3) (1 1 1) (2))
(map last (map 'mc vectors)) ;=> ("A.com" "B.com" "C.com")
What few people know is, that indexing a list also can be mapped by mapping the data structure like a function on to the list of indexes. In this case 'mc' is an complex nested data structure with all urls on a different level, but all are found. Note that 'mc' must be quoted in the mapping expression.
Re: XML parsing problems
Posted: Sun Nov 08, 2009 10:26 pm
by itistoday
Lutz wrote:Code: Select all
(map last (map 'mc vectors)) ;=> ("A.com" "B.com" "C.com")
What few people know is, that indexing a list also can be mapped by mapping the data structure like a function on to the list of indexes. In this case 'mc' is an complex nested data structure with all urls on a different level, but all are found. Note that 'mc' must be quoted in the mapping expression.
That is nifty! :-)
