Add function to invert constraints and ranges #91

[TG1999]

Signed-off-by: Tushar Goel tushar.goel.dav@gmail.com

We have invert of every operator:

>= : <
<= : >
!= : =
< : >=
> : <=
= : !=

But we don't have any inversion for star operator currently, what should we do for that ?

[TG1999]

@pombredanne I made inversion of each comparator here:

INVERTED_COMPARATORS = {
    ">=": "<",
    "<=": ">",
    "!=": "=",
    "<": ">=",
    ">": "<=",
    "=": "!=",
    "*": "^",
    "^": "*",
}

would like to get your opinion on this

[pombredanne]

Thanks... see some comments for your review

[pombredanne]

Thanks!
see my review inline for your consideration.
IMHO the inversion should be first a method on a constraint and then second a range method that use the constraints method.
We would need a few unit tests rather than only data driven tests, and we could get fewer tests by removing duplicated tests.

[pombredanne]

Thanks. Here are a few extra nit pickings for your consideration.

[pombredanne]

You need tests for the lower level constraint.invert e.g., for https://github.com/nexB/univers/pull/92/files#diff-c77d34029ce1991650937489359eef45029f37be4f1f27c21f56e50e64209d9aR138 too

[TG1999]

Done!

[pombredanne]

LGTM!
👍