Explicitly check if an override exists instead of ImportError

If an override depended on another module and it did not
exist then the raised ImportError was consumed and assumed
to mean that the override did not exist. This makes it
difficult to diagnose issues with overrides.

This uses pkgutil.get_loader() as it is the easier way to
determine if a module exists in both Python 2 and 3
and avoid deprecated functions.

https://bugzilla.gnome.org/show_bug.cgi?id=749532

1 files changed, 15 insertions, 2 deletions

diff --git a/gi/overrides/__init__.py b/gi/overrides/__init__.py
index bc915b28..942e6ede 100644
--- a/gi/overrides/__init__.py
+++ b/gi/overrides/__init__.py
@@ -2,6 +2,7 @@ import types
 import warnings
 import importlib
 import sys
+from pkgutil import get_loader
 
 from gi import PyGIDeprecationWarning
 from gi._gi import CallableInfo
@@ -107,10 +108,22 @@ def load_overrides(introspection_module):
     modules[namespace] = proxy
 
     try:
+        override_package_name = 'gi.overrides.' + namespace
+
+        # http://bugs.python.org/issue14710
         try:
-            override_mod = importlib.import_module('gi.overrides.' + namespace)
-        except ImportError:
+            override_loader = get_loader(override_package_name)
+
+        except AttributeError:
+            override_loader = None
+
+        # Avoid checking for an ImportError, an override might
+        # depend on a missing module thus causing an ImportError
+        if override_loader is None:
             return introspection_module
+
+        override_mod = importlib.import_module(override_package_name)
+
     finally:
         del modules[namespace]
         del sys.modules[module_key]