On Sat, Sep 30, 2017 at 08:37:35PM +0300, Алексей Алексей wrote:
> Hi,
>
> Can't understand the results of the following xpath queries:
>
> from lxml import etree
> from io import StringIO
> s = '<aaa><bbb>f<ccc>e</ccc>d</bbb></aaa>'
> tree = etree.parse(StringIO(s))
> print(tree.xpath('//bbb[.="fed"]')) #Returns nothing
> print(tree.xpath('//bbb[contains(.,"fed")]')) #Returns bar
> print(tree.xpath('//bbb[normalize-space(.)="fed"]')) #Returns bar
> print(tree.xpath('//bbb[string-length(.)=3]')) #Returns bar
>
> The first query doesn't find bar element by its string-value while the
> other three surprisingly do. Suppose that it is a bug.
One thing to note: the first one compares a *nodeset* using equality
against a string. The other 3 compare strings with strings for equality.
The definitions are there:
https://www.w3.org/TR/xpath/#booleans
"If one object to be compared is a node-set and the other is a string,
then the comparison will be true if and only if there is a node in
the node-set such that the result of performing the comparison on the
string-value of the node and the other string is true."
I also assume when you say "Returns bar" you really mean "Returns bbb"
thinkpad2:~/XML -> cat tst.xml
<aaa><bbb>f<ccc>e</ccc>d</bbb></aaa>
thinkpad2:~/XML -> xmllint --shell tst.xml
/ > xpath //bbb[.="fed"]
Object is a Node Set :
Set contains 0 nodes:
/ > xpath //bbb[contains(.,"fed")]
Object is a Node Set :
Set contains 1 nodes:
1 ELEMENT bbb
/ > xpath //bbb="fed"
Object is a Boolean : false
/ > xpath string(//bbb)
Object is a string : fed
/ > xpath //bbb
Object is a Node Set :
Set contains 1 nodes:
1 ELEMENT bbb
/ >
hum ... XPath computes the string value correctly. there is something
going on there.
Daniel
> I have already asked about the issue in the lxml mailing list and they
> suggested to ask here because the XPath implementation is in libxml2,
> not in lxml.
>
> The versions used:
> lxml.etree: (4, 0, 0, 0)
> libxml used: (2, 9, 5)
> libxml compiled: (2, 9, 5)
> libxslt used: (1, 1, 30)
> libxslt compiled: (1, 1, 30)
>
> Reproduction of the bug using xmllint instead of lxml:
> $ echo '<aaa><bbb>f<ccc>e</ccc>d</bbb></aaa>' | \
> xmllint --xpath '//bbb[. = "fed"]' -
> XPath set is empty
>
> Thanks in advance for any help!
>
> Aleksei
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> [email protected]
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--
Daniel Veillard | Red Hat Developers Tools http://developer.redhat.com/
[email protected] | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
http://veillard.com/ | virtualization library http://libvirt.org/
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