Why does using import on two files/modules at once giving me errors, but not when I only do it on one?

Question

Please help! I am new to Python and very confused about why my module import works one direction but not the return direction as well. In essence I can import from classes.py to mainProg.py but not from mainProg.py to classes.py and it makes no sense. I need the classes.py file to call the "newTitle()" function in the mainProg.py but as soon as i add an import to call the funtion i get these errors:

Traceback (most recent call last):
  File "C:\Users\jonathan\PycharmProjects\test\mainProg.py", line 2, in <module>
    import classes
  File "C:\Users\jonathan\PycharmProjects\test\classes.py", line 3, in <module>
    from mainProg import newTitle
  File "C:\Users\jonathan\PycharmProjects\test\mainProg.py", line 19, in <module>
    menubar = classes.menuButtons(root)
AttributeError: module 'classes' has no attribute 'menuButtons'

Process finished with exit code 1

mainProg.py

from tkinter import *
import classes

title = Label(pArea, text="*No File Loaded*")

def newTitle():
    title["text"] = classes.filename

classes.py (version 1 No Error)

from tkinter import *
from tkinter.filedialog import askopenfilename

def newFile():
    Tk().withdraw() 
    filename = askopenfilename()
    print(filename)

classes.py (version 2 Error)

from tkinter import *
from tkinter.filedialog import askopenfilename
from mainProg import newTitle

def newFile():
    Tk().withdraw() 
    filename = askopenfilename()
    newTitle()
    print(filename)

For ease of viewing, I only included relevant lines.