TypeError: 'numpy.float64' object is not callable

Hi there, 

I tried your codes, however got the following errors:
```
72     def evaluation_count_decorator(self, f, x):
     73         self.evaluation_count += 1
---> 74         return f(x)
     75 
     76 

TypeError: 'numpy.float64' object is not callable
```
Could you pls guide me on this?

Many thanks,
Thang