It's documented in the datetime module [1]: in Boolean contexts, a time object is considered to be true if and only if, after converting it to minutes and

It's documented in the datetime module [1]: in Boolean contexts, a time object is considered to be true if and only if, after converting it to minutes and subtracting utcoffset() (or 0 if that’s None), the result is non-zero. But the only reason I know that is because I read a substantial part of the exchange where Mr. Paul Moore quotes it. My initial reaction was to think "How the heck would you deduce midnight from this?" and I think arguing that the behavior is fully documented from this line alone is a bit of a stretch. It's true that it is documented, but not in a manner that is immediately obvious. Worse, there are 87 instances of "None" on that page, which makes searching for a specific issue somewhat daunting. The irony (in terms of an unexpected side effect) is that by having the discussion they did, even if nothing comes of it in terms of fixes or changes, future developers bit by this behavior will be able to readily find it via a search for midnight, None values from time objects, etc. [1] http://docs.python.org/3.4/library/datetime.html#time-objects http://docs.python.org/3.4/library/datetime.html#time-object... Edit: Left off the citation. Sorry. ;)