[MRG] Support kwargs for response.xpath()

[redapple]

Allow passing named variables and namespaces dict arguments on .xpath() shortcut, now that scrapy/parsel#45 is merged

[codecov-io]

Codecov Report

Merging #2457 into master will not impact coverage.

@@           Coverage Diff           @@
##           master    #2457   +/-   ##
=======================================
  Coverage   83.49%   83.49%           
=======================================
  Files         161      161           
  Lines        8787     8787           
  Branches     1289     1289           
=======================================
  Hits         7337     7337           
  Misses       1203     1203           
  Partials      247      247

Impacted Files	Coverage Δ
scrapy/http/response/text.py	97.22% <100%> (ø)	✅

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[kmike]

+1 to have it; it'd be nice to have docs for this feature right in Scrapy docs.

[redapple]

@kmike , I updated the docs on Selectors with XPath variables.
Do you want to mention ad-hoc namespaces too?

[kmike]

In setup.py we declare parsel >= 0.9.5, but this feature requires parsel >= 1.1.0. Time to bump version in setup.py?

[kmike]

No opinion about ad-hoc namespaces, I'm fine with whatever you decide :)

[redapple]

Is it strictly needed? For those not using kwargs, 0.9.5<=parsel<1.1 should work fine.
I thought setup.py was about the absolute minimum required version.
No strong opinion on that though, since parsel 1.1 is better.

[kmike]

We have two options:

1. document that this feature requires a more recent parsel;
2. bump parsel version.

(2) looks like a no-brainer for me - parsel is a pure-Python package, and there are no breaking changes, while (1) requires user to think twice and check what's this 'parsel' thing and what is the installed version :)

[kmike]

👍