expressions to support offsets in custom date formats

[dbcSolid]

I use ElevenClock in my organization to display the current work week (%W) using the custom formatting options (it's very useful thanks!). Unfortunately my organization uses a different definition of work week so some years there is an off by one error. It looks like ElevenClock uses the strftime C function which defines week 1 as starting on the first Monday. There is an ISO standard (ISO 8601) that defines things differently (Week 1 is the first week with a majority of its days in Jan), and my org uses a third definition.

My recommendation is to allow offsets/expressions in the custom data formatting to solve this problem more generally. e.g

%a {%W+1}.%w to add 1 week

I imagine it could be useful for other offsets I'm not thinking of.

I'm open to other solutions, but I have already implemented a fix for myself using a simple evaluation function that supports basic addition and subtraction inside {}'s as above that wraps the calls to strftime.

If there is interest I would be happy to create a pull request so others could benefit. It's a relatively small change, but I personally know a bunch of folks that would find it very useful.

Thanks!

[marticliment]

if you wanted to PR your solution, I'll merge it and release a new version with the changes in the following days!

[dbcSolid]

pull request created! Please feel free to refactor as needed (I added the expression evaluator to tools.py)

[marticliment]

Thanks!