would crash if get_home() returns None

[mdboom]

See http://bugs.debian.org/719384 for original reports.

ATM get_home() would return None if none of the home directories current exists, even though e.g. HOME environment variable is set.
As a result os.path.join would spit out exception since it was not devised to have any opinion about None.

IMHO the logic here should be fixed and get_home should not return None even if a directory pointed to by HOME environment variable on a POSIX platform is defined

[SnarkBoojum]

I just had a look at the sources ; in lib/matplotlib/init.py:

def _get_home():
    """Find user's home directory if possible.
    Otherwise, returns None.

    :see:  http://mail.python.org/pipermail/python-list/2005-February/325395.html
    """
    try:
        path = os.path.expanduser("~")
    except ImportError:
        # This happens on Google App Engine (pwd module is not present).
        pass
    else:
        if os.path.isdir(path):
            return path
    for evar in ('HOME', 'USERPROFILE', 'TMP'):
        path = os.environ.get(evar)
        if path is not None and os.path.isdir(path):
            return path
    return None

so it is looking into environment variables...

[mdboom]

I agree that crashing strangely in os.path.join is bad, but what should it do if the home directory doesn't exist? Create it? I'm not sure that's the best idea either. If $HOME points to a non-existent directory, generally that means something is wrong (and we should probably raise a better exception, but I'm not sure blindly returning it is the answer).

[SnarkBoojum]

Ooohh... I had misread the original bug report... I had understood the code wasn't finding the home even though it was explicit... and now I see that $HOME points to something invalid!

[yarikoptic]

Well I have filed a report instead of a PR because for me all the ambiguity where TMP could be the "home" is not clear. Imho $HOME is the home if it exists or not. On POSIX systems I guess HOME variable is always there... If this all was due to platform differences -- then code should reflect it. Now it just looks like a heuristic to me to get some directory to write to... then may be it should mktemp directory and return it as home if none among others was found

[pelson]

One very pertinent PR relating to this: #1824

[mdboom]

Yeah, I think your suggestion to return mktemp in the failure case is the right one.

[WeatherGod]

I have a very vague recollection of an issue reported once by a user that
did not have a writable filesystem available. Are we undoing a fix here?

[mdboom]

@WeatherGod: #1824 is one such issue. I think what's happened here is I broke support for that when I moved to using XDG directories on Linux. It looks, on further reflection, like we need to go the longer route and handle the case where get_home returns None everywhere it is called.