Mailman 3 Introduce a boundary parameter for typing.get_type_hints when used with a class object - Python-ideas

4 Aug 2020

      In one of my projects I'm reusing class-level type annotations to identify relevant attributes for serialization, e.g. similar to the following:

    attrs = {name: getattr(obj, name) for name in get_type_hints(type(obj))}

This is convenient because it merges the type annotations from the various stages in the class hierarchy, e.g.

    class Base:
        a: int
    class Derived(Base):
        b: str

results in `attrs == dict(a=..., b=...)`.

However it becomes inconvenient if external base classes are involved that define their own, unrelated type annotations, e.g.

    class External:  # from some other distribution
        unrelated: float
    class Base(External):
        a: int

It would be helpful if `get_type_hints` had a `boundary` parameter that, when used with a class object, determines the upper boundary for the MRO. So it could be used in the following way:

    get_type_hints(type(derived_obj), boundary=Base)

to exclude any type annotations further up the class hierarchy (including the ones from `Base`).

Regarding the implementation this would effectively skip over base classes in the reverse MRO until it reaches the `boundary`.

What do you think?

Introduce a boundary parameter for typing.get_type_hints when used with a class object

Dominik Vilsmeier

David Mertz

Guido van Rossum

Dominik Vilsmeier

Guido van Rossum

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