.. _`tmpdir handling`:

Temporary directories and files
================================================

The 'tmpdir' test function argument
-----------------------------------

You can use the ``tmpdir`` function argument 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::

    $ py.test test_tmpdir.py
    =========================== test session starts ============================
    platform linux2 -- Python 2.7.1 -- pytest-2.2.4
    collecting ... collected 1 items
    
    test_tmpdir.py F
    
    ================================= FAILURES =================================
    _____________________________ test_create_file _____________________________
    
    tmpdir = local('/tmp/pytest-23/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 0.02 seconds =========================

.. _`base temporary directory`:

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::

    py.test --basetemp=mydir

When distributing tests on the local machine, ``py.test`` 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.

.. _`py.path.local`: http://pylib.org/path.html