Excluding code from coverage.py¶
You may have code in your project that you know won’t be executed, and you want to tell coverage.py to ignore it. For example, you may have debugging-only code that won’t be executed during your unit tests. You can tell coverage.py to exclude this code during reporting so that it doesn’t clutter your reports with noise about code that you don’t need to hear about.
Coverage.py will look for comments marking clauses for exclusion. In this code, the “if debug” clause is excluded from reporting:
a = my_function1() if debug: # pragma: no cover msg = "blah blah" log_message(msg, a) b = my_function2()
Any line with a comment of “pragma: no cover” is excluded. If that line introduces a clause, for example, an if clause, or a function or class definition, then the entire clause is also excluded. Here the __repr__ function is not reported as missing:
class MyObject(object): def __init__(self): blah1() blah2() def __repr__(self): # pragma: no cover return "<MyObject>"
Excluded code is executed as usual, and its execution is recorded in the coverage data as usual. When producing reports though, coverage.py excludes it from the list of missing code.
When measuring branch coverage, a conditional will not be counted as a branch if one of its choices is excluded:
def only_one_choice(x): if x: blah1() blah2() else: # pragma: no cover # x is always true. blah3()
else clause is excluded, the
if only has one possible next
line, so it isn’t considered a branch at all.
Coverage.py identifies exclusions by matching lines against a list of regular expressions. Using configuration files or the coverage API, you can add to that list. This is useful if you have often-used constructs to exclude that can be matched with a regex. You can exclude them all at once without littering your code with exclusion pragmas.
For example, you might decide that __repr__ functions are usually only used in debugging code, and are uninteresting to test themselves. You could exclude all of them by adding a regex to the exclusion list:
[report] exclude_lines = def __repr__
For example, here’s a list of exclusions I’ve used:
[report] exclude_lines = pragma: no cover def __repr__ if self.debug: if settings.DEBUG raise AssertionError raise NotImplementedError if 0: if __name__ == .__main__.: class .*\bProtocol\):
Note that when using the
exclude_lines option in a configuration file, you
are taking control of the entire list of regexes, so you need to re-specify the
default “pragma: no cover” match if you still want it to apply.
A similar pragma, “no branch”, can be used to tailor branch coverage measurement. See Branch coverage measurement for details.