Summary:

1. Don't apply automatic style fixes; it bloats the patch and makes it much harder to review
2. UsingDecimal the way you're using it is inherently unsafe due to unknown contextual precision, and will make the code slower to boot. Find a way to do your work withint when usingfloat becomes impossible. Bonus: It won't make importingdatetime force you to loadDecimal in the process (a relatively heavyweight module)
3. Several comparison and hash functions aren't using the submicrosecond data, so the extra data gets ignored, which seems like a problem.
4. You broke pickling. Please don't do that.
5. (A biggy I couldn't comment on inline) This only changes the Python leveldatetime module, that CPython itself doesn't even use, by and large. Any change to the Python level code indatetime.py requires a complementary change in_datetimemodule.c so the C accelerated version of the module has the same behavior (you may have avoided at least a few test failures because they were testing the C module and didn't notice the broken code in the Python module)