+def prepend_extension(filename, ext, expected_real_ext=None):
+ name, real_ext = os.path.splitext(filename)
+ return (
+ '{0}.{1}{2}'.format(name, ext, real_ext)
+ if not expected_real_ext or real_ext[1:] == expected_real_ext
+ else '{0}.{1}'.format(filename, ext))
+
+
+def replace_extension(filename, ext, expected_real_ext=None):