Function Annotations giving error in python?

问题

So I made a function, and wanted to add annotations to it, and the compiler keeps giving me an error:

def square_root(x:number, eps:number) -> float:
    pass

And the compiler returns this:

  File "/Users/albertcalzaretto/Google Drive/CSC148H1/e1/e1a.py", line 1
    def square_root(x, eps) -> float:
                            ^
SyntaxError: invalid syntax

I've never used function annotations, and I've read several sources about it, and I don't think what I'm doing is wrong.

回答1:

Two things:

1. You must be using Python 2.x somehow. Function annotations are only supported in Python 3.x. If you try to use them in Python 2.x, you will get a SyntaxError:

   >>> def f() -> int:
     File "<stdin>", line 1
       def f() -> int:
               ^
   SyntaxError: invalid syntax
   >>>
   

2. If number is undefined (which I believe it is), then you need to make it a string so that you don't get a NameError. Below is a demonstration:

   >>> def square_root(x:number, eps:number) -> float:
   ...     pass
   ...
   Traceback (most recent call last):
     File "<stdin>", line 1, in <module>
   NameError: name 'number' is not defined
   >>>
   >>> def square_root(x:'number', eps:'number') -> float:
   ...     pass
   ...
   >>>
   

来源：https://stackoverflow.com/questions/21170521/function-annotations-giving-error-in-python