open a file using filename = browse_file_save_as() but if canceled end function

from tkinter.filedialog import *
def browse_file_open():
    selected_filename =  askopenfilename(filetypes=(("CSV files", "*.csv")
                                              ,("All files", "*.*") ))
    if selected_filename is None:
        print('canceled')
        return
    print('selected_filename = ', selected_filename)
    return selected_filename