remove .keys() to avoid creating a tmp list/keyview obj

[s-sanjay]

This is a small straight forward refactor to avoid creating a list or keyview object ( list in 2.x and key in 3.x ).
There are other folders where this change can be made but starting with commands folder.

[s-sanjay]

the test seems to only fail in py35-pinned env... weird..

[codecov]

Codecov Report

Merging #4031 into master will not change coverage.
The diff coverage is 0%.

@@           Coverage Diff           @@
##           master    #4031   +/-   ##
=======================================
  Coverage   85.67%   85.67%           
=======================================
  Files         165      165           
  Lines        9726     9726           
  Branches     1461     1462    +1     
=======================================
  Hits         8333     8333           
  Misses       1136     1136           
  Partials      257      257

Impacted Files	Coverage Δ
scrapy/commands/parse.py	20.21% <0%> (-0.12%)	⬇️
scrapy/commands/runspider.py	75.36% <0%> (+1.07%)	⬆️

[Gallaecio]

The 2nd and 3rd changes seem straightforward to me, but I wonder what is the impact of the first change (max_level) in performance.

[s-sanjay]

The 2nd and 3rd changes seem straightforward to me, but I wonder what is the impact of the first change (max_level) in performance.

so performance wise we are avoiding creating a dynamic list of size of both the list.
we loop through both the dict, and take the max and take max of that max.
earlier we loop through both the dict and create combined new list of keys and then find max in that list.

[s-sanjay]

@Gallaecio can this be merged ?

[Gallaecio]

We’ll need at least 1 more approval before merging.