Thinking about this, perhaps the bug is that Python 3 doesn't have a future_builtins module? Consider:


$ python2.6
Python 2.6.8 (unknown, Sep 28 2013, 12:09:28) 
[GCC 4.6.3] on linux3
Type "help", "copyright", "credits" or "license" for more information.
>>> from __future__ import with_statement
>>> from __future__ import print_function
>>> from future_builtins import map, zip
>>> quit()


versus:


$ python3.3
Python 3.3.2 (default, Sep 28 2013, 12:00:20) 
[GCC 4.6.3] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from __future__ import with_statement
>>> from __future__ import print_function
>>> from future_builtins import map, zip
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ImportError: No module named 'future_builtins'
>>> quit()


The expectation from the __future__ imports is that once a feature is part of Python, the import is a harmless no-op. You could expect the same from  future_builtins as well.