Created 24 May 2009, last updated 6 March 2010

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 product code are being exercised by tests, and which are not.

The latest version is 3.3.1, released 6 March 2010. It is supported on Python 2.3 through 3.1.

Quick start

Getting started is easy:

  1. Install coverage.py from the coverage page on the Python Package Index, or by using “easy_install coverage”. You may need to install the python-dev support files, for example with “apt-get install python-dev”.

  2. Use coverage run to execute your program and gather data:

    $ coverage run my_program.py arg1 arg2
    blah blah ..your program's output.. blah blah

  3. Use coverage report to report on the results:

    $ coverage report -m
    Name                      Stmts   Exec  Cover   Missing
    -------------------------------------------------------
    my_program                   20     16    80%   33-35, 39
    my_other_module              56     50    89%   17-23
    -------------------------------------------------------
    TOTAL                        76     66    87%

  4. For a nicer presentation, use coverage html to get annotated HTML listings detailing missed lines:

    $ coverage html

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

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 while running tests. For example, nose has a cover plug-in.

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

History

Coverage.py was originally written by Gareth Rees. Since 2004, Ned Batchelder has extended and maintained it with the help of many others.

More information

Next: Coverage command line usage »