What does -> do in python

Question

I saw a python example today and it used -> for example this was what I saw:

spam = None
bacon = 42
def monty_python(a:spam,b:bacon) -> "different:":
    pass

What is that code doing? I'm not quite sure I've never seen code like that I don't really get what

 a:spam,b:bacon  

is doing either, can someone explain this for me? I googled, "what does -> do in python" but no good searches came up that I found.

Answer 1

It is function annotation for a return type. annotations do nothing inside the code, they are there to help a user with code completion (in my experience).

Here is the PEP for it.

Let me demonstrate, what I mean by "annotations do nothing inside the code". Here is an example:

def fun(a: str, b: int) -> str:
    return 1

if __name__ == '__main__':
    print(fun(10, 10))

The above code will run without any errors. but as you can see the first parameter should be a string, and the second an int. But, this only is a problem in my IDE, the code runs just fine:

Answer 2

They're function annotations. They don't really do anything by themselves, but they can be used for documentation or in combination with metaprogramming.