Xpath with namespace and position

[knit-bee]

I noticed that it is not possible to use elem.find or elem.findall with an xpath that contains position indices if the method is called with the namespaces argument.
This behavior has also been reported in Bug #1873886.

It appears that during the tokenization of the xpath, the numbers are treated as tags, i.e. they are concatenated with the default namespace (during function calls with namespaces). This results in a wrong path imo.
For example:

>>> from lxml import etree
>>> doc = etree.XML("""
      <foo xmlns="http://example.com/foo">
        <bar>baz</bar>
      </foo>""")
>>> path = "./bar[1]"
>>> doc.find(path, namespaces={None:"http://example.com/foo"})
None

The target element is not found here because the path that is used is effectively:
./{http://example.com/foo}bar[{http://example.com/foo}1]

Changes:

• I added a check during the tokenization of the xpath to determine whether the processed tag is a number to avoid concatenation with the namespace.

[scoder]

Thanks. I think we should reduce the amount of code that we add here, though.

[scoder]

Given how many examples you add here, this seems worth its own custom assert method: .assertFindallEqual(element, path, expected, namespaces=None).

Also, do we actually need to add these tests? ISTM that we could get away with running the existing tests three times, once without namespaces dict, once with an empty one, and once with a non-empty one.

[knit-bee]

Thank you for the review, I will try to include your suggestions next week.

[scoder]

Thanks for this PR, I have integrated it in e950468 but implemented the tests differently.