I can reproduce the bug in 3.5.0+ Ubuntu with list iterator, if I execute python with -S:

    % python3.5 -S
    Python 3.5.0+ (default, Oct 11 2015, 09:05:38) 
    [GCC 5.2.1 20151010] on linux
    >>> format(iter([]))
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    TypeError: Type list_iterator doesn't define __format__

Thus here it depends on the stuff that site does or doesn't do. Iterating over a list iterator does *not* trigger the initialization. Printing it doesn't help either, or anything else that does not touch the non-magic attributes. I am not even sure what the site.py and such are doing to the list iterator class to trigger the initialization.