Function measure 

pub fn measure(
    root: &Path,
    base: &str,
    thresholds: Thresholds,
    omit: &[String],
) -> Result<Outcome>

Diff-scoped Python coverage floor (#162): measure thresholds over the <base>...HEAD changed .py lines instead of the whole tree. omit is the coverage-rule exemptions, as in crate::coverage::measure — an exempt file is omitted from the run, so its changed lines drop out of the ratio.

Scopes to .py sources and returns early — with no coverage run — when the diff touches none, so a PR that changes only docs or other languages doesn’t pay for a measurement (and is vacuously covered). Requires coverage.py + pytest + git; an unresolvable base surfaces as an error rather than a silent pass.