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On 26 October 2017 at 07:30, Chris Barker <chris.barker@noaa.gov> wrote:

+1 on a classmethod constructor

+0 on a based-on-type default constructor

+inf on SOMETHING!

Let's get passed the bike shedding and make this work!

I'll also note that these aren't either/or outcomes: adding a str-specific classmethod \*doesn't\* preclude implicitly calling that class method from the default constructor later based on the input type.

For example, decimal.Decimal.from\_float() was added before the type constructor gained native support for float inputs, due to concerns about potential binary-vs-decimal rounding errors arising from doing such conversions implicitly.

So we can add "datetime.fromisoformat(isotime: str)" now, and then \*if\* we later decide to support the "type(x)(str(x)) == x" numeric invariant for the datetime classes, that can be specified as "If the constructor arguments consist of a single string, that is handled by calling the fromisoformat class method".

Cheers,

Nick.

Nick Coghlan | ncoghlan@gmail.com | Brisbane, Australia