Use pgi only when gi is not available

- Write a convenience utility to handle the import process.

plinth/modules/networks/forms.py

@@ -20,9 +20,8 @@ from django.core import validators
 from django.utils.translation import ugettext_lazy as _
 
 from plinth import network
-import pgi
+from plinth.utils import import_from_gi
-pgi.require_version('NM', '1.0')
+nm = import_from_gi('NM', '1.0')
-from pgi.repository import NM as nm
 
 
 def _get_interface_choices(device_type):

plinth/network.py

@@ -21,17 +21,15 @@ Helper functions for working with network manager.
 
 import collections
 from django.utils.translation import ugettext_lazy as _
-import pgi
-pgi.require_version('GLib', '2.0')
-from pgi.repository import GLib as glib
-pgi.require_version('NM', '1.0')
-from pgi.repository import NM as nm
 import logging
 import socket
 import struct
 import subprocess
 import uuid
 
+from plinth.utils import import_from_gi
+glib = import_from_gi('GLib', '2.0')
+nm = import_from_gi('NM', '1.0')
 
 logger = logging.getLogger(__name__)
 

plinth/package.py

@@ -22,15 +22,13 @@ Framework for installing and updating distribution packages
 from django.contrib import messages
 from django.utils.translation import ugettext as _
 import functools
-import pgi
-pgi.require_version('GLib', '2.0')
-from pgi.repository import GLib as glib
-pgi.require_version('PackageKitGlib', '1.0')
-from pgi.repository import PackageKitGlib as packagekit
 import logging
 import threading
 
 import plinth
+from plinth.utils import import_from_gi
+glib = import_from_gi('GLib', '2.0')
+packagekit = import_from_gi('PackageKitGlib', '1.0')
 
 
 logger = logging.getLogger(__name__)

plinth/utils.py

@@ -0,0 +1,36 @@
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+"""
+Miscelleneous utility method.
+"""
+
+import importlib
+
+
+def import_from_gi(library, version):
+    """Import and return a GObject introspection library."""
+    try:
+        import gi as package
+        package_name = 'gi'
+    except ImportError:
+        import pgi as package
+        package_name = 'pgi'
+
+    package.require_version(library, version)
+
+    return importlib.import_module(package_name + '.repository.' + library)