get_type_hints() always raises on forward references · Issue #508 · python/typing (original) (raw)

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Description

ericvsmith/dataclasses#92 (comment) raised an important question (this existing problem is also mentioned in PEP 563). Currently, get_type_hints will raise a NameError in situations where it might not be the desired behaviour (e.g. if used by a class decorator). For example:

def modify(cls): types = get_type_hints(cls) # do something with 'cls' and 'types' return cls

@modify class C: linked: 'C'

It looks like it will be useful to have an option to keep forward references that are currently undefined. For example:

class C: x: 'ClassVar[B]'

assert get_type_hints(C, allow_forward=True) == {'x': ClassVar['B']}

class B: ...

assert get_type_hints(C, allow_forward=True) == {'x': ClassVar[B]}