Typing, how come that :int is not ensuring int parameter?

[Barry Scott]

> On 11 Jun 2020, at 21:51, zljubisic at gmail.com wrote:
> 
> Hi,
> 
> If I run this code:
> class Property:
> 
>    def __init__(self, var: int):
>        self.a: int = var
> 
>    @property
>    def a(self):
>        return self.__a
> 
>    @a.setter
>    def a(self, var: int):
>        if var > 0 and var % 2 == 0:
>            self.__a = var
>        else:
>            self.__a = 2
> 
> if __name__ == '__main__':
>    x = Property(1.5)
>    print(x.a)
> 
> I am getting 2.
> How come, if I have created a class with :int in order to ensure that "a" property must be an integer, that I can create an instance with float (1.5)?

The : int is a type *hint* that isn not enforced by python.

If you use a checker program like  mypy it will use the type hints and report problems to your.

You can install myy with pip.

$ python3 -m pip install mypy

I put your code in a.py and then checked it:

$ /Library/Frameworks/Python.framework/Versions/3.8/bin/mypy a.py
a.py:18: error: Argument 1 to "Property" has incompatible type "float"; expected "int"
Found 1 error in 1 file (checked 1 source file)

As you can see it found the problem.

Barry



> 
> Regards.
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>