Support total=False for protocols

[ilevkivskyi]

I have heard few requests to allow this:

class SomeDimensions(Protocol, total=False):
    x: float
    y: float
    z: float
    ct: float

with exactly the same semantics as for TypedDicts (including subclassing so that only part of members can be optional).

This is quite straightforward to implement. I am just leaving this here so we will not forget about this feature request.

[intgr]

Supporting PEP 655 NotRequired[] for Protocols would also be very cool and more flexible.

PEP 544 currently states about this:

We can come up with examples where it would be handy to be able to say that a method or data attribute does not need to be present in a class implementing a protocol, but if it is present, it must conform to a specific signature or type. One could use a hasattr() check to determine whether they can use the attribute on a particular instance.

Languages such as TypeScript have similar features and apparently they are pretty commonly used. The current realistic potential use cases for protocols in Python don’t require these. In the interest of simplicity, we propose to not support optional methods or attributes. We can always revisit this later if there is an actual need.

[intgr]

Related discussion in python/typing project:

• Optional class and protocol fields and methods typing#601