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")

Asked By: Gaurang Shah

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Answer 1

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.

Answered By: Frank T

Answer 2

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

Answered By: yugal sinha

difference between fixture and yield_fixture in pytest

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