Coverage.py

Coverage.py is a tool for measuring code coverage of Python programs. It monitors your program, noting which parts of the code have been executed, then analyzes the source to identify code that could have been executed but was not.

Coverage measurement is typically used to gauge the effectiveness of tests. It can show which parts of your code are being exercised by tests, and which are not.

The latest version is coverage.py 5.0b2, released December 8, 2019. It is supported on:

  • Python versions 2.7, 3.5, 3.6, 3.7, 3.8, and 3.9 alpha.

  • PyPy2 7.2.0 and PyPy3 7.2.0.

This is a pre-release build. The usual warnings about possible bugs apply. The latest stable version is coverage.py 4.5.4, described here.

For Enterprise

Available as part of the Tidelift Subscription.
Coverage and thousands of other packages are working with Tidelift to deliver one enterprise subscription that covers all of the open source you use. If you want the flexibility of open source and the confidence of commercial-grade software, this is for you. Learn more.

Quick start

Getting started is easy:

  1. Install coverage.py:

    $ pip install coverage
    

    For more details, see Installation.

  2. Use coverage run to run your test suite and gather data. However you normally run your test suite, you can run your test runner under coverage. If your test runner command starts with “python”, just replace the initial “python” with “coverage run”.

    Instructions for specific test runners:

    If you usually use:

    $ pytest arg1 arg2 arg3
    

    then you can run your tests under coverage with:

    $ coverage run -m pytest arg1 arg2 arg3
    

    Many people choose to use the pytest-cov plugin, but for most purposes, it is unnecessary.

    Change “python” to “coverage run”, so this:

    $ python -m unittest discover
    

    becomes:

    $ coverage run -m unittest discover
    

    Nose has been unmaintained for a long time. You should seriously consider adopting a different test runner.

    Change this:

    $ nosetests arg1 arg2
    

    to:

    $ coverage run -m nose arg1 arg2
    

    To limit coverage measurement to code in the current directory, and also find files that weren’t executed at all, add the --source=. argument to your coverage command line.

  3. Use coverage report to report on the results:

    $ coverage report -m
    Name                      Stmts   Miss  Cover   Missing
    -------------------------------------------------------
    my_program.py                20      4    80%   33-35, 39
    my_other_module.py           56      6    89%   17-23
    -------------------------------------------------------
    TOTAL                        76     10    87%
    
  4. For a nicer presentation, use coverage html to get annotated HTML listings detailing missed lines:

    $ coverage html
    

    Then open htmlcov/index.html in your browser, to see a report like this one.

Using coverage.py

There are a few different ways to use coverage.py. The simplest is the command line, which lets you run your program and see the results. If you need more control over how your project is measured, you can use the API.

Some test runners provide coverage integration to make it easy to use coverage.py while running tests. For example, pytest has the pytest-cov plugin.

You can fine-tune coverage.py’s view of your code by directing it to ignore parts that you know aren’t interesting. See Specifying source files and Excluding code from coverage.py for details.

Getting help

If the FAQ doesn’t answer your question, you can discuss coverage.py or get help using it on the Testing In Python mailing list.

Bug reports are gladly accepted at the GitHub issue tracker. GitHub also hosts the code repository.

Professional support for coverage.py is available as part of the Tidelift Subscription.

I can be reached in a number of ways. I’m happy to answer questions about using coverage.py.