Changed testing for the presence of optional modules,

because simply testing a file with a ".so" extension
does not work on multiarch Python installations.

Signed-off-by: Slávek Banko <slavek.banko@axis.cz>
(cherry picked from commit b34531364d)

module-init.py

@@ -12,6 +12,23 @@ for m_path in sys.path:
 for m_path in tqt_modules:
     sys.path.insert(0, m_path)
 
+# Checking if the module is available
+def is_module_available(module_name):
+    if sys.version_info < (3, 0):
+        # python 2
+        import pkgutil
+        mod_loader = pkgutil.find_loader(module_name)
+    if sys.version_info <= (3, 3):
+        # python 3.0 to 3.3
+        import pkgutil
+        mod_loader = pkgutil.find_loader(module_name)
+    elif sys.version_info >= (3, 4):
+        # python 3.4 and above
+        import importlib.util
+        mod_loader = importlib.util.find_spec(module_name)
+
+    return mod_loader is not None
+
 # Base modules
 __all__ = [
  'qt',
@@ -24,11 +41,11 @@ __all__ = [
 ]
 
 # Optional modules
-if os.path.exists(os.path.join(m_pyqt_dir, 'qtaxcontainer.so')):
+if is_module_available('qtaxcontainer'):
     __all__.append('qtaxcontainer')
-if os.path.exists(os.path.join(m_pyqt_dir, 'qtext.so')):
+if is_module_available('qtext'):
     __all__.append('qtext')
-if os.path.exists(os.path.join(m_pyqt_dir, 'qtgl.so')):
+if is_module_available('qtgl'):
     __all__.append('qtgl')
 
 # Import namespaces