:nth-last-child selector incorrectly starts at 0 instead of 1

[calebj0seph]

Using cssselect 0.9.1, the :nth-last-child selector starts from 0 instead of 1, that is, :nth-last-child(0) selects the last element when it should instead select nothing.

Here is an example using lxml:

import lxml.html

html_fragment = lxml.html.fromstring("""
<div>
    <p>First</p>
    <p>Second</p>
    <p>Second Last</p>
    <p>Last</p>
</div>
""")

for element in html_fragment.cssselect("div > p:nth-last-child(1)"):
    print(element.text_content())

print()

for element in html_fragment.cssselect("div > p:nth-last-child(2n)"):
    print(element.text_content())

Output:

Second Last

Second
Last

Expected output:

Last

First
Second Last

[SimonSapin]

Thanks for the report! To be honest I’m unlikely to fix this myself. I believe the entire approach of translating Selectors to XPath is flawed (see #12 (comment) for example), and so I don’t really want to do more work on cssselect. I’ve started cssselect2 that implements Selectors "for real", but it’s blocked on some non-obvious design decisions: Kozea/cssselect2#1

I’d review a pull request, though.

[redapple]

@Dobz , #42 also fixes your example. It doesn't fix #12 though

[redapple]

Fixed in #60