Improve performance of linerange

[Krock21]

I found that the bandit is running very slow on the file long_set.py
I added some caching for linerange function

Feel free to comment and propose a better solution

See time measurements down below

[ericwb]

Can you please attach the file long_set.py, so I can compare as well for the review? Thanks!

[Krock21]

Can you please attach the file long_set.py, so I can compare as well for the review? Thank

Sure!
https://github.com/Krock21rus/bandit/blob/cache_linerange/examples/long_set.py

[Krock21]

Ok, I measured it again:
Pure version from master:
command():

git clean -d -f -x && cp ~/long_set.py examples/long_set.py && virtualenv -p python3 bandit-env && source bandit-env/bin/activate && pip3 install -r requirements.txt && python3 setup.py install && time ./bandit-env/bin/bandit examples/long_set.py

result:

Run started:2021-01-09 12:40:26.826760
Test results:
	No issues identified.
Code scanned:
	Total lines of code: 7278
	Total lines skipped (#nosec): 0
Run metrics:
	Total issues (by severity):
		Undefined: 0.0
		Low: 0.0
		Medium: 0.0
		High: 0.0
	Total issues (by confidence):
		Undefined: 0.0
		Low: 0.0
		Medium: 0.0
		High: 0.0
Files skipped (0):

real	0m57,304s
user	0m56,296s
sys	0m0,478s

updated version from Krock21rus:cache_linerange(this pull request)
Just checkout branch and run it, long_set.py is already added to examples

command:

git clean -d -f -x && virtualenv -p python3 bandit-env && source bandit-env/bin/activate && pip3 install -r requirements.txt && python3 setup.py install && time ./bandit-env/bin/bandit examples/long_set.py

result:

Run started:2021-01-09 12:43:17.356068
Test results:
	No issues identified.
Code scanned:
	Total lines of code: 7278
	Total lines skipped (#nosec): 0
Run metrics:
	Total issues (by severity):
		Undefined: 0.0
		Low: 0.0
		Medium: 0.0
		High: 0.0
	Total issues (by confidence):
		Undefined: 0.0
		Low: 0.0
		Medium: 0.0
		High: 0.0
Files skipped (0):

real	0m1,000s
user	0m0,982s
sys	0m0,008s

57s -> 1s on a single long_set with 7276 'a' elements

[ericwb]

Very noticeable improvement. Nicely done. However, I do think most of this linerange() func becomes redundant with Python 3.8 included end_lineno on nodes.