human
Here are class variables and instance variables given the following:
I am working on the file "Lesson_02_classes_object_oriented.ipynb".
The first task is:
What are class variables and instance variables?
Class variables are variables attached to the definition of a class. Simply, they are just regular variable definitions inside a class
Instance variables are variables created for each instance of a class. We denote them by adding "self." in front of them. 
Examples:
Can you write Python code for it?
assistant
#Here are class variables and instance variables.

class ClassI:
    # Define instance variables in a special method, called a "constructor", that defines what happens when an object is created.
    def __init__(self):
        self.a = 1
        self.b = 2

class ClassC:
    # Define class variables normally. They are here, whether you create an object or not.
    a = 3
    b = 44

instance_of_ClassC = ClassC()
print instance_of_ClassC.a, instance_of_ClassC.b 

print ClassC.a

instance_of_ClassI = ClassI()
print instance_of_ClassI.a, instance_of_ClassI.b

# This will cause an error, because to access instance variables, you need an instance of class!
print ClassI.a