from tkinter import *
from tkinter import ttk

main = Tk()

def printframe(event):
    frame_name = book.tabs()[event.widget.index("current")] #todo: identify the name of the frame in a way that works even with the custom Notebook that has X buttons.
    frame = book.nametowidget(frame_name)
    print(frame, type(frame))

book = ttk.Notebook(main)
book.bind("<<NotebookTabChanged>>", printframe)
book.grid()

for x in range(5):
    tabname = 'Book tab that has been cut short'
    if len(tabname) > 10:
        tabname = ''.join(tabname[:10])
    frame = Frame(book, width=200, height=200)
    Label(frame, text=f'This is tab {x}').grid(padx=50, pady=50, sticky=NSEW)
    book.add(frame, text=f'{tabname}')

main.mainloop()