Add Deme.size_at() to compute the deme size at a given time.

[grahamgower]

Closes #312.

[codecov]

Codecov Report

Merging #314 (7c9950b) into main (083dcea) will increase coverage by 0.08%.
The diff coverage is 100.00%.

❗ Current head 7c9950b differs from pull request most recent head a9db443. Consider uploading reports for the commit a9db443 to get more accurate results

@@            Coverage Diff             @@
##             main     #314      +/-   ##
==========================================
+ Coverage   98.15%   98.24%   +0.08%     
==========================================
  Files           8        8              
  Lines        1573     1595      +22     
==========================================
+ Hits         1544     1567      +23     
+ Misses         29       28       -1     

Impacted Files	Coverage Δ
demes/demes.py	100.00% <100.00%> (ø)
demes/hypothesis_strategies.py	98.68% <100.00%> (+0.73%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 083dcea...a9db443. Read the comment docs.

[apragsdale]

Looking good - just a small suggestion for the error message.

[jeromekelleher]

Maybe it's the sleep deprivation, but I can't get my head around this condition - shouldn't it be epoch.start_time <= time < epoch.end_time? As in, we break if the time is within this epoch's interval?

[grahamgower]

Two things: (1) start_time > end_time, so we must have start_time > time >= end_time. And (2) we also want to accept time=math.inf, so we check start_time >= time >= end_time. Given this is in a loop, and the epochs are time-sorted, the start_time == time condition is only hit for the first epoch, and only if the time is infinity.

[jeromekelleher]

Ack, I'm thinking backwards in time as usual, thanks, my bad!