difference between fixture and yield_fixture in pytest

Question

I am going through pytest fixtures, and the following looks pretty similar, latest works pretty similar.

Yes, the readability is better in yield_fixure, however could someone let me know what exactly is the difference.

which should I use, in cases like mentioned below?

@pytest.fixture()
def open_browser(request):
    print("Browser opened")

    def close_browser():
        print("browser closed")

    request.addfinalizer(close_browser)

    return "browser object"

@pytest.yield_fixture()
def open_browser():
    print("Browser opened")
    yield "browser object"
    print("browser closed")


def test_google_search(open_browser):
    print(open_browser)
    print("test_google_search")

A `yield` fixture makes using context managers in fixtures natural — anthony sottile, Aug 17 '17 at 14:58
As of pytest 3.0.0 (2016-08-18), `@pytest.fixture` with yield statements is the preferred way to write teardown code and `@pytest.yield_fixture` is deprecated (but not yet removed). Read more [here](https://docs.pytest.org/en/6.2.x/changelog.html#id1313). — Yash Nag, May 20 '21 at 07:26

Frank T · Answer 1 · 2017-08-17T17:43:03.053

The only difference is in readability. I think (though I'm not 100% sure) the underlying behavior is identical (i.e. the cleanup after the yield statement is run as a finalizer). I always prefer using yield fixtures for cleanup, since it's more readable.

If you're using pytest <3.0, you'll still need to use pytest.yield_fixture to get that behavior. But if you're able to use pytest 3.0+, pytest.yield_fixture is deprecated and you can use pytest.fixture to get the same yield_fixture behavior.

Here are the explanatory docs:

Since pytest-3.0, fixtures using the normal fixture decorator can use a yield statement to provide fixture values and execute teardown code, exactly like yield_fixture in previous versions.

Marking functions as yield_fixture is still supported, but deprecated and should not be used in new code.

Incorrect. Look here https://github.com/pytest-dev/pytest/issues/2508 to see yield does not tear down if setup fails — Jinglesting, Sep 29 '19 at 14:20

score 14 · Accepted Answer · edited Mar 29 '19 at 11:39

14

addfinalizer has two key differences over yield:

It is possible to register multiple finalizer functions.
Finalizers will always be called regardless if the fixture setup code raises an exception. This is handy to properly close all resources created by a fixture even if one of them fails to be created/acquired

From the pytest docs

edited Mar 29 '19 at 11:39

Nino Filiu

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answered Mar 29 '19 at 11:19

yugal sinha

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difference between fixture and yield_fixture in pytest

2 Answers2