Using type hints to ensure that two function parameters are of the same type

Question

Say I have a function that retrieves a value from a source, then maps it to another type before returning it.

An example function declaration might look like this:

def get_value(mapping_function: Callable[[str], any]) -> any:
    # ...

The function would retrieve the value from some source and then map it according to the mapping_function before returning the result.

Is there any way I can specify that the returned type and the result of the lambda would be of the same type? It could be any type, but it will always be the same, something like the following:

def get_value(mapping_function: Callable[[str], T]) -> T:
    # ...

For example, in Java, I could do:

public static <T> T getValue(Function<String, T> mappingFunction) {
  // ...
}

Maybe I wrap it in a class with a generic type or something?

This is discussed in the typing module's documentation on Generics. — Andrew Eckart
– Andrew Eckart, Commented Jun 17, 2021 at 22:09

sturgemeister · Accepted Answer · 2021-06-17 22:10:23Z

2

should be:

from typing import TypeVar

T = TypeVar('T')

def get_value(mapping_function: Callable[[str], T]) -> T:
    # ...

answered Jun 17, 2021 at 22:10

sturgemeister

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1 Comment

sturgemeister Over a year ago

positional arguments will constrain the type from Any to some list: T = TypeVar('T', int, float, complex)

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