Catching up... On 1/8/21 11:51 AM, Guido van Rossum wrote:> On Thu, Jan 7, 2021 at 11:35 PM David Foster <davidfstr@gmail.com
<mailto:davidfstr@gmail.com>> wrote:
A1. On 1/6/21 3:54 AM, Tuukka Mustonen wrote: > Why I am after something else than your earlier proposal of: > > class MyThing(TypedDict, total=False): > req1: Required[int] > opt1: str > req2: Required[float] > > ...is that people _expect_ it to work the other way around. It feels > more natural if the stuff you define is expected to exist, and you then > mark up what differs from that. That's how ~everything else already > works and I would say that's how our brain are already tuned.
Agreed. I would think "required" would be assumed to be the default, and "not-required" would be the special case that needs marking.
But "required" *is* the default -- you have to specify `total=False` to make fields non-required.
I think I've finally wrapped my head around this comment. In long-form: * If you have a TypedDict with total=True (the default), then all keys are required. * If you have a TypedDict with total=False, then all keys become not-required by default. * Therefore introducing a Required[...] form is a backward-compatible way of marking certain keys of a total=False TypedDict as *required*, which currently isn't possible to do. It bends my brain a bit: If I want to create an entirely new TypedDict with some keys required and some keys not-required then I must: (1) declare a total=False TypedDict and (2) explicitly mark the keys I want required with Required[...] and (3) remember that in this context all unmarked keys are NOT-required. (This is backwards from TypeScript which essentially always declares TypedDicts as total=True but then only marks certain keys as NOT-required using the "name?: type" syntax.) I suppose total=False TypedDicts bend my brain a bit anyway: It strikes me as odd that a single keyword at the top can flip the default required-ness of every key in the dictionary. However the total=False syntax is here now and I don't think it's going away, so we might as well work with it. Long story short: I think Required[...] on a total=False TypedDict would be reasonable, given that the total=False syntax already exists. +0.5 Also, Required[...] satisfies: ✅ Single word. Easy to type. ✅ Is in positive form, rather than a "not X" or "no X" negative form. ✅ Does not "put funny syntax before the colon" -- David Foster | Seattle, WA, USA Contributor to TypedDict support for mypy