Fix python3 compatibility issues with doc fix

xbob/math/__init__.py

@@ -2,5 +2,4 @@ from ._library import __version__
 from ._library import *
 
 # gets sphinx autodoc done right - don't remove it
-__all__ = [k for k in dir() if not k.startswith('_')]
-del k
+__all__ = [_ for _ in dir() if not _.startswith('_')]