How to call setup once for all tests and teardown after all are finished

The OP’s requirement was for setup and teardown each to execute only once, not one time per module. This can be accomplished with a combination of a conftest.py file, @pytest.fixture(scope="session") and passing the fixture name to each test function.

These are described in the Pytest fixtures documentation

Here’s an example:

conftest.py

import pytest

@pytest.fixture(scope="session")
    def my_setup(request):
        print '\nDoing setup'
        def fin():
            print ("\nDoing teardown")
        request.addfinalizer(fin)

test_something.py

def test_dummy(my_setup):
    print '\ntest_dummy'

test_something2.py

def test_dummy2(my_setup):
    print '\ntest_dummy2'

def test_dummy3(my_setup):
    print '\ntest_dummy3'

The output when you run py.test -s:

collected 3 items 

test_something.py 
Doing setup

test_dummy
.
test_something2.py 
test_dummy2
.
test_dummy3
.
Doing teardown

The name conftest.py matters: you can’t give this file a different name and expect Pytest to find it as a source of fixtures.

Setting scope="session" is important. Otherwise setup and teardown will be repeated for each test module.

If you’d prefer not to pass the fixture name my_setup as an argument to each test function, you can place test functions inside a class and apply the pytest.mark.usefixtures decorator to the class.