__file__ is sometimes absolute, sometimes relative

Discussion in 'Python' started by Sébastien Barthélemy, Oct 1, 2010.

  1. Hello,

    I use a data file that lies on disk in the same directory that the
    module which makes use of it.

    The data file is checked in the repository and gets installed by
    the distutils ``package_data`` directive, so it is in place both
    during development and after and install.

    In my program, I need to find the absolute path to this data file.

    I could think of 3 ways to do this:
    1. using the __path__ property in the module
    2. using __file__ property in the module
    3. using __file__ and os.getcwd() in the module

    The first option does not work, because __path__ is initialised after the
    module is loaded (apparently).

    Solution 2 works, but behaves differently when ran from python or
    from a doctest file. The path in __file__ is absolute if the program
    is ran directly by ``python``, and relative if it is ran by
    ``python -m doctest``.

    Solution 3 works. However if there is a better way to do this, please let me
    know.

    I could not find anything documenting what the proper value for __file__
    should be. Maybe my problem with solution 2 is a bug in doctest or runpy?

    I put up a simple example exhibiting the problem.

    Here are the results on my mac (using python from macport)
    I get the same results using python 2.6, 2.7 and 3.1

    $ python2.6 test.py
    /Users/seb/Devel/arboris-python/src/pyfile
    /Users/seb/Devel/arboris-python/src/pyfile/mod.pyc
    /Users/seb/Devel/arboris-python/src/pyfile
    /Users/seb/Devel/arboris-python/src/pyfile

    $ python2.6 -m doctest test.txt
    **********************************************************************
    File "test.txt", line 5, in test.txt
    Failed example:
    print mod.__file__
    Expected:
    /Users/seb/Devel/arboris-python/src/pyfile/mod.pyc
    Got:
    mod.pyc
    **********************************************************************
    File "test.txt", line 7, in test.txt
    Failed example:
    print(mod.whereami)
    Expected:
    /Users/seb/Devel/arboris-python/src/pyfile
    Got:
    <BLANKLINE>
    **********************************************************************
    File "test.txt", line 9, in test.txt
    Failed example:
    print(mod.whereami2)
    Expected:
    /Users/seb/Devel/arboris-python/src/pyfile
    Got:
    /Users/seb/Devel/arboris-python/src/pyfile/
    **********************************************************************
    1 items had failures:
    3 of 6 in test.txt
    ***Test Failed*** 3 failures.

    Cheers
    Sebastian
     
    Sébastien Barthélemy, Oct 1, 2010
    #1
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  2. I have used the following, but I don't know either if it is a good way:

    os.path.dirname(os.path.realpath(__file__))
     
    Arnaud Delobelle, Oct 1, 2010
    #2
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