Switch between two frames in tkinter using a separate file for each page

Question

I've created a tkinter app, which has three pages: StartPage, PageOne and PageTwo. From StartPage you can go to PageOne and to PageTwo, whereas from PageOne and PageTwo, you can go back to StartPage. To implement it, I am using the technique described by Steven Vascellaro in this post Switch between two frames in tkinter.

This is the code provided by Steven:

# Multi-frame tkinter application v2.2
import tkinter as tk

class SampleApp(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)
        self._frame = None
        self.switch_frame(StartPage)

    def switch_frame(self, frame_class):
        """Destroys current frame and replaces it with a new one."""
        new_frame = frame_class(self)
        if self._frame is not None:
            self._frame.destroy()
        self._frame = new_frame
        self._frame.pack()


class StartPage(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        start_label = tk.Label(self, text="This is the start page")
        page_1_button = tk.Button(self, text="Open page one",
                                  command=lambda: master.switch_frame(PageOne))
        page_2_button = tk.Button(self, text="Open page two",
                                  command=lambda: master.switch_frame(PageTwo))
        start_label.pack(side="top", fill="x", pady=10)
        page_1_button.pack()
        page_2_button.pack()


class PageOne(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        page_1_label = tk.Label(self, text="This is page one")
        start_button = tk.Button(self, text="Return to start page",
                                 command=lambda: master.switch_frame(StartPage))
        page_1_label.pack(side="top", fill="x", pady=10)
        start_button.pack()


class PageTwo(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        page_2_label = tk.Label(self, text="This is page two")
        start_button = tk.Button(self, text="Return to start page",
                                 command=lambda: master.switch_frame(StartPage))
        page_2_label.pack(side="top", fill="x", pady=10)
        start_button.pack()


if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()

Now, I am trying to make this code modular and place each page in a separate python file. This is how I split the Steven's code between three Python files (start_page.py, page_one.py, page_two.py):

start_page.py:

import tkinter as tk
from page_one import PageOne
from page_two import PageTwo


class SampleApp(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)
        self._frame = None
        self.switch_frame(StartPage)

    def switch_frame(self, frame_class):
        """Destroys current frame and replaces it with a new one."""
        new_frame = frame_class(self)
        if self._frame is not None:
            self._frame.destroy()
        self._frame = new_frame
        self._frame.pack()


class StartPage(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        start_label = tk.Label(self, text="This is the start page")
        page_1_button = tk.Button(self, text="Open page one",
                                  command=lambda: master.switch_frame(PageOne))
        page_2_button = tk.Button(self, text="Open page two",
                                  command=lambda: master.switch_frame(PageTwo))
        start_label.pack(side="top", fill="x", pady=10)
        page_1_button.pack()
        page_2_button.pack()


if __name__ == "__main__":
    app = SampleApp()
    app.mainloop()

page_one.py:

import tkinter as tk
from start_page import StartPage

class PageOne(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        page_1_label = tk.Label(self, text="This is page one")
        start_button = tk.Button(self, text="Return to start page",
                                 command=lambda: master.switch_frame(StartPage))
        page_1_label.pack(side="top", fill="x", pady=10)
        start_button.pack()

page_two.py:

import tkinter as tk
from start_page import StartPage

class PageTwo(tk.Frame):
    def __init__(self, master):
        tk.Frame.__init__(self, master)

        page_2_label = tk.Label(self, text="This is page two")
        start_button = tk.Button(self, text="Return to start page",
                                 command=lambda: master.switch_frame(StartPage))
        page_2_label.pack(side="top", fill="x", pady=10)
        start_button.pack()

The problem is here the class StartPage depends on PageOne and PageTwo, while PageOne and PageTwo depend on StartPage. This leads to the error described in this post ImportError: Cannot import name X.

Is there a way in tkinter to keep the described functionality, but to allow each page to be located in a separate python file?