How to indicate that a function expects a function as a parameter, or returns a function, via function annotations?

Question

You can use function annotations in python 3 to indicate the types of the parameters and return value, like so:

def myfunction(name: str, age: int) -> str:
    return name + str(age) #usefulfunction

But what if you were writing a function that expects a function as a parameter, or returns one?

I realize that you can write any valid expression in for the annotations, so I could write "function" as a string, but is that the best/only way of doing it? Is there nothing like the built-in types int/float/str/list/dict etc? I'm aware of callable, but I'm wondering if there's anything else.

Answer 1

There's no style defined for annotations. Either use callable, types.FunctionType or a string.

PS: callable was not available in Python 3.0 and 3.1

Answer 2

Very interesting... I've never even heard of function annotations in Python 3. The following code in the interpreter suggests you might use function in place of str and int. Just my two cents.

>>> a = lambda x: x*2
>>> type(a)
<class 'function'>