adding license + some filename cleanup
diff --git a/elftools/common/utils.py b/elftools/common/utils.py
index 7aa1cd9..e0a4cfe 100644
--- a/elftools/common/utils.py
+++ b/elftools/common/utils.py
@@ -6,6 +6,7 @@
 # Eli Bendersky (eliben@gmail.com)
 # This code is in the public domain
 #-------------------------------------------------------------------------------
+from contextlib import contextmanager
 from .exceptions import ELFParseError, ELFError, DWARFError
 from ..construct import ConstructError
 
@@ -71,13 +72,6 @@
     _assert_with_exception(cond, msg, DWARFError)
 
 
-def _assert_with_exception(cond, msg, exception_type):
-    if not cond:
-        raise exception_type(msg)
-
-
-from contextlib import contextmanager
-
 @contextmanager
 def preserve_stream_pos(stream):
     """ Usage:
@@ -91,3 +85,10 @@
     yield
     stream.seek(saved_pos)
 
+
+#------------------------- PRIVATE -------------------------
+
+def _assert_with_exception(cond, msg, exception_type):
+    if not cond:
+        raise exception_type(msg)
+