What is wrong this wrapper (decorator)?

[fl]

On Saturday, November 14, 2015 at 12:23:50 PM UTC-5, fl wrote:
> Hi,
> 
> I follow a tutorial to learn decorator:
> 
> http://simeonfranklin.com/blog/2012/jul/1/python-decorators-in-12-steps/
> 
> I use Enthought Canopy to run the following code.
> It is really strange that the wrapper does not take effect. 
> In fact, I go back to the basic way (not with @):
> 
> wrapper(sub(two, one))
> Out[38]: <function checker>
> 
> 
> When I use the non-wrapper mode, it has Coord print out.
> If I use wrapper, it has nothing to print out.
> Due to no debug mode help, I don't see anything wrong yet.
> 
> 
> (add(two, one))
>                                           # nothing print out
> (sub(two, three))
> Out[43]: Coord:-- {'y': 300, 'x': 400}    # correct is here
> 
> 
> Anyone can help?
> Thanks,
> 
> 
> 
> ............
> class Coordinate(object):
>     def __init__(self, y, x):
>         self.y = y
>         self.x = x
>     def __repr__(self):
>         return "Coord:-- " + str(self.__dict__)
> 
> def add(a, b):
>     return Coordinate(a.x + b.x, a.y + b.y)
> 
> def sub(a, b):
>     return Coordinate(a.x - b.x, a.y - b.y)
> 
> def wrapper(func):
>     def checker(a, b): # 1
>         if a.x < 0 or a.y < 0:
>             a = Coordinate(a.x if a.x > 0 else 0, a.y if a.y > 0 else 0)
>             if b.x < 0 or b.y < 0:
>                 b = Coordinate(b.x if b.x > 0 else 0, b.y if b.y > 0 else 0)
>             ret = func(a, b)
>             if ret.x < 0 or ret.y < 0:
>                 ret = Coordinate(ret.x if ret.x > 0 else 0, ret.y if ret.y > 0 else 0)
>             return ret
>     return checker
>     
> one = Coordinate(100, 200)
> two = Coordinate(300, 200)
> three = Coordinate(-100, -100)
> 
> add = wrapper(add)
> #sub = wrapper(sub)

Excuse me. I just realize that the indent made the logic incorrect.
It is different from other language. Thanks.