Support kwargs for loader.*_xpath()

[alexander-matsievsky]

Allow passing named variables and namespaces dict arguments on ItemLoader.*_xpath() family of methods (add_xpath, etc.).

Related scrapy/scrapy#2457.

[kmike]

See also: scrapy/scrapy#2950

[wRAR]

I think this was done in #48?

[VMRuiz]

@wRAR I would say yes.

However, I think is not added for *_css() methods. Does it make sense to implement it there too?

[Gallaecio]

Hmm… Does CSS syntax support variables, though? This may be XPath-specific.

[Gallaecio]

If not, we may want to consider removing **kw from the _get_cssvalues signature, so I think it makes sense to keep this open either way.

[VMRuiz]

There is no references to CSS variables in Parsel lib, so I guess there is no user case for this.

[VMRuiz]

If not, we may want to consider removing **kw from the _get_cssvalues signature, so I think it makes sense to keep this open either way.

Let's create a new issue for that to avoid having issues open forever 😄