How to use temporary directories and files in tests

The tmp_path fixture

You can use the tmp_path fixture which will provide a temporary directory unique to the test invocation, created in the base temporary directory.

tmp_path is a pathlib.Path object. Here is an example test usage:

# content of test_tmp_path.py
CONTENT = "content"


def test_create_file(tmp_path):
    d = tmp_path / "sub"
    d.mkdir()
    p = d / "hello.txt"
    p.write_text(CONTENT)
    assert p.read_text() == CONTENT
    assert len(list(tmp_path.iterdir())) == 1
    assert 0

Running this would result in a passed test except for the last assert 0 line which we use to look at values:

$ pytest test_tmp_path.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-7.x.y, pluggy-1.x.y
rootdir: /home/sweet/project
collected 1 item

test_tmp_path.py F                                                   [100%]

================================= FAILURES =================================
_____________________________ test_create_file _____________________________

tmp_path = PosixPath('PYTEST_TMPDIR/test_create_file0')

    def test_create_file(tmp_path):
        d = tmp_path / "sub"
        d.mkdir()
        p = d / "hello.txt"
        p.write_text(CONTENT)
        assert p.read_text() == CONTENT
        assert len(list(tmp_path.iterdir())) == 1
>       assert 0
E       assert 0

test_tmp_path.py:11: AssertionError
========================= short test summary info ==========================
FAILED test_tmp_path.py::test_create_file - assert 0
============================ 1 failed in 0.12s =============================

The tmp_path_factory fixture

The tmp_path_factory is a session-scoped fixture which can be used to create arbitrary temporary directories from any other fixture or test.

For example, suppose your test suite needs a large image on disk, which is generated procedurally. Instead of computing the same image for each test that uses it into its own tmp_path, you can generate it once per-session to save time:

# contents of conftest.py
import pytest


@pytest.fixture(scope="session")
def image_file(tmp_path_factory):
    img = compute_expensive_image()
    fn = tmp_path_factory.mktemp("data") / "img.png"
    img.save(fn)
    return fn


# contents of test_image.py
def test_histogram(image_file):
    img = load_image(image_file)
    # compute and test histogram

See tmp_path_factory API for details.

The tmpdir and tmpdir_factory fixtures

The tmpdir and tmpdir_factory fixtures are similar to tmp_path and tmp_path_factory, but use/return legacy py.path.local objects rather than standard pathlib.Path objects. These days, prefer to use tmp_path and tmp_path_factory.

See tmpdir tmpdir_factory API for details.

The default base temporary directory

Temporary directories are by default created as sub-directories of the system temporary directory. The base name will be pytest-NUM where NUM will be incremented with each test run. Moreover, entries older than 3 temporary directories will be removed.

The number of entries currently cannot be changed, but using the --basetemp option will remove the directory before every run, effectively meaning the temporary directories of only the most recent run will be kept.

You can override the default temporary directory setting like this:

pytest --basetemp=mydir

Warning

The contents of mydir will be completely removed, so make sure to use a directory for that purpose only.

When distributing tests on the local machine using pytest-xdist, care is taken to automatically configure a basetemp directory for the sub processes such that all temporary data lands below a single per-test run basetemp directory.