I took a moment to scan the datetime documentation. The behavior of str() on timedelta objects is very consistent, and matches the internal representation. From the docs:
str(t) Returns a string in the form [D day[s], ][H]H:MM:SS[.UUUUUU], where D is negative for negative t. (5) Note (5) reads: String representations of timedelta objects are normalized similarly to their internal representation. This leads to somewhat unusual results for negative timedeltas. Feel free to submit a patch to improve str(t), where t is negative, though as Chris suggested, hashing this out on python-ideas would be a good idea. I suggest you start with some concrete examples. There are, as I see it, two common cases where t is negative: -1 day < t < 0 and t <= -1 day Skip -- https://mail.python.org/mailman/listinfo/python-list
