Temporary directories and files

The ‘tmpdir’ fixture

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

tmpdir is a py.path.local object which offers os.path methods and more. Here is an example test usage:

# content of test_tmpdir.py
import os
def test_create_file(tmpdir):
    p = tmpdir.mkdir("sub").join("hello.txt")
    p.write("content")
    assert p.read() == "content"
    assert len(tmpdir.listdir()) == 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_tmpdir.py
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-3.x.y, py-1.x.y, pluggy-0.x.y
rootdir: $REGENDOC_TMPDIR, inifile:
collected 1 item

test_tmpdir.py F                                                     [100%]

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

tmpdir = local('PYTEST_TMPDIR/test_create_file0')

    def test_create_file(tmpdir):
        p = tmpdir.mkdir("sub").join("hello.txt")
        p.write("content")
        assert p.read() == "content"
        assert len(tmpdir.listdir()) == 1
>       assert 0
E       assert 0

test_tmpdir.py:7: AssertionError
========================= 1 failed in 0.12 seconds =========================

The ‘tmpdir_factory’ fixture

New in version 2.8.

The tmpdir_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 tmpdir, you can generate it once per-session to save time:

# contents of conftest.py
import pytest


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


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

See 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.

You can override the default temporary directory setting like this:

pytest --basetemp=mydir

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