On Thu, Aug 27, 2015 at 8:13 AM, Ethan Furman <ethan@stoneleaf.us> wrote: [Alexander Belopolsky]
OK, so datetime module itself will never set fold=-1. In the list
below, can you mark the methods that need to be patched to check the fold attribute in your preferred design:
[Ethan Furman] datetime.__new__ YES datetime.combine YES (could have a time instance with fold=None) datetime.replace YES datetime.strptime only if `fold=` is allowed [Ethan Furman]
If `fold=None` is present /when attempting to create a datetime/ that is
ambiguous or invalid, an exception is raised /at that moment/ meaning that a datetime with `fold=None` /will never exist/. fold=None` /will not be the default/. I don't grasp the significance of the slashes in your text above, but it looks like your idea is similar to the one I outlined in the "Strict Invalid Time Checking: an idea for another PEP" thread. As I said there, it is workable, but there are many details that need to be thought out before this idea becomes PEP-worthy. Let's move the discussion of those details to a thread that does not have PEP 495 in the subject. Feel free to reuse my thread or open a new one. What we can do in PEP 495 is tighten the language about acceptable values for the fold= argument in replace(). Since pure python implementation currently allows None for year through microsecond arguments, we have the following text in the PEP: """ In CPython, any non-integer value of fold [passed to replace()] will raise a TypeError , but other implementations may allow the value None to behave the same as when fold is not given. """ I am fine with removing this text and leaving fold=None option open for the future PEPs to explore.