What do you call this type of parameter?

[league55]

In some code I've seen stuff like this:

1 2	def some_function(a -> int):     #do something

I thought a -> int was called a decorator, but a decorator seems to be this:

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def some_function(func):     def some_func(*args):         #do something to func         return func(*args)     return some_func   @some_function def some_other_function(params):     #do something

So if a -> int is not a decorator, what's it called and what does it do?

[snippsat]

It's type hints added in Python 3.5.
So it's hints and not forced yet maybe in 3.7.

So if run in Python 3.6 no error massage is generated,
have to use 3-party library like mypy to get a error message about wrong types.
Example:
hello.py

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def greeting(name: str) -> str:     return f'Hello {name}'   print(greeting('Kent'))

hello_int.py

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def greeting(name: str) -> str:     return f'Hello {name}'   print(greeting(100))

With mypy pip install mypy

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E:\1 λ mypy hello.py # No error   E:\1 λ mypy hello_int.py hello_int.py:4: error: Argument 1 to "greeting" has incompatible type "int"; expected "str"

[league55]

Can I use the type hints to do type checking without mypy? (Or I guess I can actually try it to find out haha.)