Self heal invalid cache files.

Fixes enthought#114

comtypes/client/_generate.py

@@ -3,6 +3,7 @@
 import sys
 import comtypes.client
 import comtypes.tools.codegenerator
+import imp
 
 import logging
 logger = logging.getLogger(__name__)
@@ -23,7 +24,11 @@ def _my_import(fullname):
     if comtypes.client.gen_dir \
            and comtypes.client.gen_dir not in comtypes.gen.__path__:
         comtypes.gen.__path__.append(comtypes.client.gen_dir)
-    return __import__(fullname, globals(), locals(), ['DUMMY'])
+
+    mod = imp.reload(eval(fullname)) if fullname in sys.modules \
+            else __import__(fullname, globals(), locals(), ['DUMMY'])
+    mod._comtypes_validate_file()
+    return mod
 
 def _name_module(tlib):
     # Determine the name of a typelib wrapper module.
@@ -152,8 +157,10 @@ def _CreateWrapper(tlib, pathname=None):
     # helper which creates and imports the real typelib wrapper module.
     fullname = _name_module(tlib)
     try:
-        return sys.modules[fullname]
-    except KeyError:
+        mod = sys.modules[fullname]
+        mod._comtypes_validate_file()
+        return mod
+    except (KeyError, AttributeError):
         pass
 
     modname = fullname.split(".")[-1]

comtypes/tools/codegenerator.py

@@ -258,6 +258,7 @@ def generate_code(self, items, filename=None):
         for line in wrapper.wrap(text):
             print >> self.output, line
         print >> self.output, "from comtypes import _check_version; _check_version(%r)" % version
+        print >> self.output, "def _comtypes_validate_file(): pass"
         return loops
 
     def type_name(self, t, generate=True):
@@ -627,7 +628,7 @@ def External(self, ext):
         modname = comtypes.client._generate._name_module(ext.tlib)
         ext.name = "%s.%s" % (modname, ext.symbol_name)
         self._externals[libdesc] = modname
-        print >> self.imports, "import", modname
+        print >> self.imports, "import %s; %s._comtypes_validate_file()" % (modname, modname)
         comtypes.client.GetModule(ext.tlib)
 
     def Constant(self, tp):