Fixture functions using “yield” / context manager integration

New in version 2.4.

pytest-2.4 allows fixture functions to seamlessly use a yield instead of a return statement to provide a fixture value while otherwise fully supporting all other fixture features.

Let’s look at a simple standalone-example using the yield syntax:

# content of

import pytest

def passwd():
    print ("\nsetup before yield")
    f = open("/etc/passwd")
    yield f.readlines()
    print ("teardown after yield")

def test_has_lines(passwd):
    print ("test called")
    assert passwd

In contrast to finalization through registering callbacks, our fixture function used a yield statement to provide the lines of the /etc/passwd file. The code after the yield statement serves as the teardown code, avoiding the indirection of registering a teardown callback function.

Let’s run it with output capturing disabled:

$ py.test -q -s

setup before yield
test called
.teardown after yield

1 passed in 0.12 seconds

We can also seamlessly use the new syntax with with statements. Let’s simplify the above passwd fixture:

# content of

import pytest

def passwd():
    with open("/etc/passwd") as f:
        yield f.readlines()

def test_has_lines(passwd):
    assert len(passwd) >= 1

The file f will be closed after the test finished execution because the Python file object supports finalization when the with statement ends.

Note that the yield fixture form supports all other fixture features such as scope, params, etc., thus changing existing fixture functions to use yield is straightforward.


While the yield syntax is similar to what contextlib.contextmanager() decorated functions provide, with pytest fixture functions the part after the “yield” will always be invoked, independently from the exception status of the test function which uses the fixture. This behaviour makes sense if you consider that many different test functions might use a module or session scoped fixture.

Discussion and future considerations / feedback

There are some topics that are worth mentioning:

  • usually yield is used for producing multiple values. But fixture functions can only yield exactly one value. Yielding a second fixture value will get you an error. It’s possible we can evolve pytest to allow for producing multiple values as an alternative to current parametrization. For now, you can just use the normal fixture parametrization mechanisms together with yield-style fixtures.
  • lastly yield introduces more than one way to write fixture functions, so what’s the obvious way to a newcomer?

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