Incremental code coverage for Python unit tests?

Brief

I use pycobertura.

pycobertura diff --format html --output cov_diff.html coverage_old.xml coverage_new.xml

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Details

I use the following chain (coverage):

1. Generate coverage report: python -m coverage run -m unittest

2. Output cobertura's XML format: coverage xml --omit tests/* -o cover_old.xml

3. -- Modify code or checkout newer commit --

4. Generate coverage report: python -m coverage run -m unittest

5. Output cobertura's XML format: coverage xml --omit tests/* -o cover_new.xml

6. Generate diff: pycobertura diff --format html --output cov_diff.html coverage_old.xml coverage_new.xml