text: from tkinter import *
  
  from backend import Database
  
  # instantiate Database
  db = Database()
  
  
  def view_command():
      list1.delete(0, END)
      for row in db.view():
          list1.insert(END, row)
  
  
  def search_command():
      list1.delete(0, END)
      for row in db.search(title_value.get(), author_value.get(), year_value.get(), isbn_value.get()):
          list1.insert(END, row)
  
  
  def add_command():
      db.insert(title_value.get(), author_value.get(), year_value.get(), isbn_value.get())
      list1.delete(0, END)
      list1.insert(END, (title_value.get(), author_value.get(), year_value.get(), isbn_value.get()))
  
  
  def get_selected_row(event):
      try:
          global selected_tuple
          index = list1.curselection()[0]
          selected_tuple = list1.get(index)
          e1.delete(0, END)
          e1.insert(END, selected_tuple[1])
          e2.delete(0, END)
          e2.insert(END, selected_tuple[2])
          e3.delete(0, END)
          e3.insert(END, selected_tuple[3])
          e4.delete(0, END)
          e4.insert(END, selected_tuple[4])
      except IndexError:
          pass
  
  
  def delete_command():
      db.delete(selected_tuple[0])
  
  
  def update_command():
      db.update(selected_tuple[0], title_value.get(), author_value.get(), year_value.get(), isbn_value.get())
  
  
  if __name__ == '__main__':
      window = Tk()
  
      window.wm_title("Bookstore")
  
      # labels
      l1 = Label(window, text="Title")
      l1.grid(row=0, column=0)
      l2 = Label(window, text="Year")
      l2.grid(row=1, column=0)
      l3 = Label(window, text="Author")
      l3.grid(row=0, column=2)
      l4 = Label(window, text="ISBN")
      l4.grid(row=1, column=2)
  
      # entries
      title_value = StringVar()
      e1 = Entry(window, textvariable=title_value)
      e1.grid(row=0, column=1)
      author_value = StringVar()
      e2 = Entry(window, textvariable=author_value)
      e2.grid(row=0, column=3)
      year_value = StringVar()
      e3 = Entry(window, textvariable=year_value)
      e3.grid(row=1, column=1)
      isbn_value = StringVar()
      e4 = Entry(window, textvariable=isbn_value)
      e4.grid(row=1, column=3)
  
      # list
      list1 = Listbox(window, height=6, width=35)
      list1.grid(row=2, column=0, rowspan=6, columnspan=2, sticky=(N, W, E, S))
  
      sb1 = Scrollbar(window, orient=VERTICAL, command=list1.yview)
      sb1.grid(row=2, column=2, rowspan=6, sticky=(N, S))
      # list1.configure(yscrollcommand=sb1.set)
      # sb1.configure(command=list1.yview)
  
      list1.bind('<<ListboxSelect>>', get_selected_row)
  
      b1 = Button(window, text="View All", width=12, command=view_command)
      b1.grid(row=2, column=3)
      b2 = Button(window, text="Search Entry", width=12, command=search_command)
      b2.grid(row=3, column=3)
      b3 = Button(window, text="Add Entry", width=12, command=add_command)
      b3.grid(row=4, column=3)
      b4 = Button(window, text="Update", width=12, command=update_command)
      b4.grid(row=5, column=3)
      b5 = Button(window, text="Delete", width=12, command=delete_command)
      b5.grid(row=6, column=3)
      b6 = Button(window, text="Close", width=12, command=window.destroy)
      b6.grid(row=7, column=3)
  
      window.mainloop()
  