[Python] Python Protocol write-only attributes

The Python documentation on Protocols (typing.Protocol) mentions the following:

By default, protocol variables as defined above are considered readable and writable. To define a read-only protocol variable, one can use an (abstract) property
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Making a protocol variable read-only is useful because it becomes covariant. So for example:

from typing import Protocol

class A(): pass
class B(A): pass

# protocols

class HasA(Protocol):
a: A # read-write

class HasA_RO(Protocol):
@property
def a(self) -> A: ... # read-only

#implementation

class Impl():
a: B



Then Impl implements HasA_RO, but not HasA. This is because

impl1: HasA = Impl() # type error
impl2: HasA_RO = Impl() # ok

a = A()

impl1.a = a # valid for HasA, but not for Impl1

impl2.a = a # is, correctly, not allowed !



Now, I would like to know if there is a way to make a protocol with write-only variables.

This would be useful because the variable would then be contravariant. For example

class HasB_WO(Protocol):

b: WriteOnly ...

class Impl2():
b: A

i2: HasB_WO = Impl2() # valid because you can always write a value of type B to a field of type A

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