Add a gettextutils.install() helper function

Part of fixing bug #995287

Every top-level script in every project needs to call gettext.install()
so that a _() builtin function is installed and strings are translated
using the correct translation domain.

However, translations are always installed in the default localedir
(which is commonly '/usr/share/locale') and, in cases like devstack, may
be found in a project-specific localedir. To support such a use case we
should have project-specific environment variables for overriding the
default value of localedir - e.g. NOVA_LOCALEDIR.

Add a new gettextutils.install() helper method to make this as easy as
possible for projects to get right.

Change-Id: I6c8549c8ff00797c96f2dd4b0b5266d18d77aa19

openstack/common/gettextutils.py

@@ -24,6 +24,7 @@ Usual usage in an openstack.common module:
 """
 
 import gettext
+import os
 
 
 t = gettext.translation('oslo', 'locale', fallback=True)
@@ -31,3 +32,19 @@ t = gettext.translation('oslo', 'locale', fallback=True)
 
 def _(msg):
     return t.ugettext(msg)
+
+
+def install(domain):
+    """Install a _() function using the given translation domain.
+
+    Given a translation domain, install a _() function using gettext's
+    install() function.
+
+    The main difference from gettext.install() is that we allow
+    overriding the default localedir (e.g. /usr/share/locale) using
+    a translation-domain-specific environment variable (e.g.
+    NOVA_LOCALEDIR).
+    """
+    gettext.install(domain,
+                    localedir=os.environ.get(domain.upper() + '_LOCALEDIR'),
+                    unicode=True)

tests/unit/test_gettext.py

@@ -17,7 +17,9 @@
 
 import logging
 
-from openstack.common.gettextutils import _
+import mock
+
+from openstack.common import gettextutils
 from tests import utils
 
 
@@ -27,4 +29,16 @@ LOG = logging.getLogger(__name__)
 class GettextTest(utils.BaseTestCase):
 
     def test_gettext_does_not_blow_up(self):
-        LOG.info(_('test'))
+        LOG.info(gettextutils._('test'))
+
+    def test_gettext_install_looks_up_localedir(self):
+        with mock.patch('os.environ.get') as environ_get:
+            with mock.patch('gettext.install') as gettext_install:
+                environ_get.return_value = '/foo/bar'
+
+                gettextutils.install('blaa')
+
+                environ_get.assert_called_once_with('BLAA_LOCALEDIR')
+                gettext_install.assert_called_once_with('blaa',
+                                                        localedir='/foo/bar',
+                                                        unicode=True)