Things that cause trouble
| history: | 20121231T085200, brand new docs. |
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Coverage works well, and I want it to properly measure any Python program, but
there are some situations it can’t cope with. This page details some known
problems, with possible courses of action, and links to coverage.py bug reports
with more information.
I would love to hear from you if you have information about any of
these problems, even just to explain to me why you want them to start working
properly.
If your problem isn’t discussed here, you can of course search the coverage.py
bug tracker directly to see if there is some mention of it.
Things that don’t work
There are a number of popular modules, packages, and libraries that prevent
coverage.py from working properly:
- execv, or one of its variants. These end the current program and replace
it with a new one. This doesn’t save the collected coverage data, so your
program that calls execv will not be fully measured. A patch for coverage.py
is in issue 43.
- multiprocessing launches processes to provide parallelism. These
processes don’t get measured by coverage.py. Some possible fixes are
discussed or linked to in issue 117.
- gevent, which is based on greenlet, and is similar to eventlet. All
of these manipulate the C stack, and therefore confuse coverage.py.
Issue 149 has some pointers to more information.
- sys.settrace is the Python feature that coverage.py uses to see what’s
happening in your program. If another part of your program is using
sys.settrace, then it will conflict with coverage.py, and it won’t be
measured properly.
Things that require –timid
Some packages interfere with coverage measurement, but you might be able to
make it work by using the --timid command-line switch, or the [run]
timid=True configuration option.
- DecoratorTools, or any package which uses it, notably TurboGears.
DecoratorTools fiddles with the trace function. You will need to use
--timid.
Really obscure things
- Python 2.5 had a bug (1569356) that could make your program behave
differently when being measured with coverage. This is diagnosed in issue 51.