python3中 ->的意義

參考網址：
https://stackoverflow.com/questions/14379753/what-does-mean-in-python-function-definitions

python3中 ->的意義

1. According to this, the example you’ve supplied:

    def f(x) -> 123:
        return x
   

will be forbidden in the future (and in current versions will be confusing), it would need to be changed to:

def f(x) -> int:
    return x

for it to effectively describe that function f returns an object of type int.

1. python中也支持parameter annotations參數註釋
   Python ignores it. In the following code:

    def f(x) -> int:
        return int(x)
   

the -> int just tells that f() returns an integer. It is called a return annotation, and can be accessed as f.annotations[‘return’].

Python also supports parameter annotations:

def f(x: float) -> int:
    return int(x)

: float tells people who read the program (and some third-party libraries/programs, e. g. pylint) that x should be a float. Itis accessed as f.annotations[‘x’], and doesn’t have any meaning by itself. See the documentation for more information: