dir/
    modA.py
    modB.py
    modC.py

import modB

instB = modB.clsB()

print("Successful")

import modC

list = [modC.clsC]

class clsB:
    def __init__(self):
        pass

from modB import clsB

instB = clsB()

class clsC(clsB):
    def __init__(self):
        pass