use XDG_CONFIG_HOME if available

priority is:

$XDG/ipython if both or neither exist
$HOME/.ipython if it exists and $XDG/ipython does not exist

closes gh-48
closes gh-246

IPython/utils/path.py

@@ -246,6 +246,24 b' def get_home_dir():'
     else:
         raise HomeDirError('No valid home directory could be found for your OS')
 
+def get_xdg_dir():
+    """Return the XDG_CONFIG_HOME, if it is defined and exists, else None.
+    
+    This is only for posix (Linux,Unix,OS X, etc) systems.
+    """
+
+    isdir = os.path.isdir
+    env = os.environ
+    
+    if os.name == 'posix':
+        # Linux, Unix, AIX, OS X
+        # use ~/.config if not set OR empty
+        xdg = env.get("XDG_CONFIG_HOME", None) or os.path.join(get_home_dir(), '.config')
+        if xdg and isdir(xdg):
+            return xdg.decode(sys.getfilesystemencoding())
+    
+    return None
+    
 
 def get_ipython_dir():
     """Get the IPython directory for this platform and user.
@@ -253,14 +271,34 b' def get_ipython_dir():'
     This uses the logic in `get_home_dir` to find the home directory
     and the adds .ipython to the end of the path.
     """
+    
+    env = os.environ
+    pjoin = os.path.join
+    exists = os.path.exists
+    
     ipdir_def = '.ipython'
+    xdg_def = 'ipython'
+    
     home_dir = get_home_dir()
+    xdg_dir = get_xdg_dir()
     # import pdb; pdb.set_trace()  # dbg
-    ipdir = os.environ.get(
-        'IPYTHON_DIR', os.environ.get(
-            'IPYTHONDIR', os.path.join(home_dir, ipdir_def)
-        )
-    )
+    ipdir = env.get('IPYTHON_DIR', env.get('IPYTHONDIR', None))
+    if ipdir is None:
+        # not set explicitly, use XDG_CONFIG_HOME or HOME
+        home_ipdir = pjoin(home_dir, ipdir_def)
+        if xdg_dir:
+            # use XDG, as long as the user isn't already
+            # using $HOME/.ipython and *not* XDG/ipython
+            
+            xdg_ipdir = pjoin(xdg_dir, xdg_def)
+        
+            if exists(xdg_ipdir) or not exists(home_ipdir):
+                ipdir = xdg_ipdir
+        
+        if ipdir is None:
+            # not using XDG
+            ipdir = home_ipdir
+    
     return ipdir.decode(sys.getfilesystemencoding())
 
 

IPython/utils/tests/test_path.py

@@ -46,6 +46,7 b' env = os.environ'
 TEST_FILE_PATH = split(abspath(__file__))[0]
 TMP_TEST_DIR = tempfile.mkdtemp()
 HOME_TEST_DIR = join(TMP_TEST_DIR, "home_test_dir")
+XDG_TEST_DIR = join(HOME_TEST_DIR, "xdg_test_dir")
 IP_TEST_DIR = join(HOME_TEST_DIR,'.ipython')
 #
 # Setup/teardown functions/decorators
@@ -59,6 +60,7 b' def setup():'
     # Do not mask exceptions here.  In particular, catching WindowsError is a
     # problem because that exception is only defined on Windows...
     os.makedirs(IP_TEST_DIR)
+    os.makedirs(os.path.join(XDG_TEST_DIR, 'ipython'))
 
 
 def teardown():
@@ -236,9 +238,93 b' def test_get_ipython_dir_2():'
     os.name = "posix"
     env.pop('IPYTHON_DIR', None)
     env.pop('IPYTHONDIR', None)
+    env.pop('XDG_CONFIG_HOME', None)
     ipdir = path.get_ipython_dir()
     nt.assert_equal(ipdir, os.path.join("someplace", ".ipython"))
 
+@with_environment
+def test_get_ipython_dir_3():
+    """test_get_ipython_dir_3, use XDG if defined, and .ipython doesn't exist."""
+    path.get_home_dir = lambda : "someplace"
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env['XDG_CONFIG_HOME'] = XDG_TEST_DIR
+    ipdir = path.get_ipython_dir()
+    nt.assert_equal(ipdir, os.path.join(XDG_TEST_DIR, "ipython"))
+
+@with_environment
+def test_get_ipython_dir_4():
+    """test_get_ipython_dir_4, use XDG if both exist."""
+    path.get_home_dir = lambda : HOME_TEST_DIR
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env['XDG_CONFIG_HOME'] = XDG_TEST_DIR
+    xdg_ipdir = os.path.join(XDG_TEST_DIR, "ipython")
+    ipdir = path.get_ipython_dir()
+    nt.assert_equal(ipdir, xdg_ipdir)
+
+@with_environment
+def test_get_ipython_dir_5():
+    """test_get_ipython_dir_5, use .ipython if exists and XDG defined, but doesn't exist."""
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env['XDG_CONFIG_HOME'] = XDG_TEST_DIR
+    os.rmdir(os.path.join(XDG_TEST_DIR, 'ipython'))
+    ipdir = path.get_ipython_dir()
+    nt.assert_equal(ipdir, IP_TEST_DIR)
+
+@with_environment
+def test_get_ipython_dir_6():
+    """test_get_ipython_dir_6, use XDG if defined and neither exist."""
+    path.get_home_dir = lambda : 'somehome'
+    path.get_xdg_dir = lambda : 'somexdg'
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    xdg_ipdir = os.path.join("somexdg", "ipython")
+    ipdir = path.get_ipython_dir()
+    nt.assert_equal(ipdir, xdg_ipdir)
+
+@with_environment
+def test_get_xdg_dir_1():
+    """test_get_xdg_dir_1, check xdg_dir"""
+    reload(path)
+    path.get_home_dir = lambda : 'somewhere'
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env.pop('XDG_CONFIG_HOME', None)
+    
+    nt.assert_equal(path.get_xdg_dir(), os.path.join('somewhere', '.config'))
+
+
+@with_environment
+def test_get_xdg_dir_1():
+    """test_get_xdg_dir_1, check nonexistant xdg_dir"""
+    reload(path)
+    path.get_home_dir = lambda : HOME_TEST_DIR
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env.pop('XDG_CONFIG_HOME', None)
+    nt.assert_equal(path.get_xdg_dir(), None)
+
+@with_environment
+def test_get_xdg_dir_2():
+    """test_get_xdg_dir_2, check xdg_dir default to ~/.config"""
+    reload(path)
+    path.get_home_dir = lambda : HOME_TEST_DIR
+    os.name = "posix"
+    env.pop('IPYTHON_DIR', None)
+    env.pop('IPYTHONDIR', None)
+    env.pop('XDG_CONFIG_HOME', None)
+    cfgdir=os.path.join(path.get_home_dir(), '.config')
+    os.makedirs(cfgdir)
+    
+    nt.assert_equal(path.get_xdg_dir(), cfgdir)
 
 def test_filefind():
     """Various tests for filefind"""