human
I am working on the file "01-IPythonHintsAndTips.ipynb".
The first task is:
Class and Instance Attributes
https://twitter.com/jakevdp/status/1120898594519650304?s=09  
Tricky Python bug I just hit due to an incorrect mental model of class \& instance attributes
Solution is to use self.__class__._num_instances += 1.
Can you write Python program for it?

Can you provide a the Python program you requested?
assistant
#Here is the Python program you requested.

class Foo:
    _num_instances = 0
    def __init__(self): 
        self._num_instances += 1 
#         self.__class__._num_instances += 1
        
f1 = Foo() 
f2 = Foo() 
print(Foo._num_instances)