CODEWITHSUNDEEP
pythontype-hintingmypy
Eric Yabs
Eric Yabs

Reputation: 11

How can I pass a type hint that MyPy will accept as a parameter to a function which defines a function internally?

I'm trying to write unit tests for types we're using with beartype, our runtime type checker. The tests run as expected, however MyPy will not accept the code.

The following code works, however the MyPy check fails.

def typecheck(val: Any, t: type):
    """
    isinstance() does not allow things like Tuple[Int]
    """

    @beartype
    def f(v: t):
        return v

    try:
        f(val)
    except BeartypeCallHintPepParamException:
        return False
    return True

# passes
def test_typecheck():
    assert typecheck((1,), Tuple[int])
    assert not typecheck((1,), Tuple[str])

However, I get the following error. The linked to page isn't helpful.

error: Variable "t" is not valid as a type
note: See https://mypy.readthedocs.io/en/latest/common_issues.html#variables-vs-type-aliases

How do I properly annotate this? Ive tried TypeVars but I get the same error.

Upvotes: 1

Views: 613

Answers (1)

chepner
chepner

Reputation: 532238

Assign the type hint directly, rather than letting it be assigned via a function annotation.

def typecheck(val, t):
    """
    isinstance() does not allow things like Tuple[Int]
    """

    @beartype
    def f(v):
        return v
    f.__annotations__['v'] = t

    try:
        f(val)
    except BeartypeCallHintPepParamException:
        return False
    return True

# passes
def test_typecheck():
    assert typecheck((1,), Tuple[int])
    assert not typecheck((1,), Tuple[str])

Upvotes: 1

Related Questions