I really like the "_exec_module" trick, but it should be applied to builtin modules as well. I hacked _sre.c and got:

~/python/cpython3.x$ ./python 
Traceback (most recent call last):
  File "/home/amauryfa/python/cpython3.x/Lib/site.py", line 70, in <module>
    import re
  File "/home/amauryfa/python/cpython3.x/Lib/re.py", line 122, in <module>
    import sre_compile
  File "/home/amauryfa/python/cpython3.x/Lib/sre_compile.py", line 13, in <module>
    import _sre, sys
  File "<frozen importlib._bootstrap>", line 1318, in _find_and_load
  File "<frozen importlib._bootstrap>", line 1285, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 347, in set_package_wrapper
  File "<frozen importlib._bootstrap>", line 360, in set_loader_wrapper
  File "<frozen importlib._bootstrap>", line 443, in _requires_builtin_wrapper
  File "<frozen importlib._bootstrap>", line 493, in load_module
ValueError: Just a test


This change correctly hides importlib frames:


diff -r 9afdd8c25bf2 Lib/importlib/_bootstrap.py
--- a/Lib/importlib/_bootstrap.py	Sun Jul 08 14:00:06 2012 +0200
+++ b/Lib/importlib/_bootstrap.py	Sun Jul 08 15:03:27 2012 +0200
@@ -490,12 +490,15 @@
         """Load a built-in module."""
         is_reload = fullname in sys.modules
         try:
-            return _imp.init_builtin(fullname)
+            return self._exec_module(fullname)
         except:
             if not is_reload and fullname in sys.modules:
                 del sys.modules[fullname]
             raise
 
+    def _exec_module(self, fullname):
+        return _imp.init_builtin(fullname)
+
     @classmethod
     @_requires_builtin
     def get_code(cls, fullname):