A case for type intersection: duck typing file-like arguments with an ad-hoc set of small protocols

Ideas
7

object was actually the first thing I tried too, but it would produce:

TypeError: duplicate base class object

And if I did:

    SupportsRead = SupportsWrite = object()

I’d get:

TypeError: object() takes no arguments

So I figured Mock() was the most convenient object because it can be called with any arguments, although one can also do:

class M:
    def __new__(*args):
        return object.__new__(M)
try:
    from _typeshed import SupportsRead, SupportsWrite
except ModuleNotFoundError:
    SupportsRead = SupportsWrite = M()

class SupportsReadWrite(SupportsRead, SupportsWrite):
    pass

At any rate this feels like an ugly workaround, having to repeat the name of every protocol in use. Better use @hauntsaninja’s useful_types even though it’s an additional dependency (or make it part of stdlib maybe?).

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