grid
method does not return; implicitly return None
.
Separate the following statement into two statements:
self.__tracksListBox = Listbox(self.__master, width=100, height=25).grid(row=0, column=1,
rowspan=4)
like:
self.__tracksListBox = Listbox(self.__master, width=100, height=25)
self.__tracksListBox.grid(row=0, column=1, rowspan=4)