Python class variables test

bad_class_var.py

class C:
    class_var = None
    def __init__(self):
        if self.class_var is None:
            self.class_var = [1]
            print('Creating new instance')
        else:
            print('Appending to existing')
            self.class_var.append(1)

c1 = C()
c2 = C()
c3 = C()

output

$python3 bad_class_var.py 
Creating new instance
Creating new instance
Creating new instance