function - Why does all indices of a list of lists change -

i writing code prints out seating arrangement , checks list of lists see if seat available (in list indicated '-' if empty) if empty replace '-' '#'. when check list of lists , replace indices @ lets [1][1] changes indices in [0][1], [2][1], [3][1]...etc. '#'

my code far:

globalseats = []  def create(rows, seats):     global globalseats     count = 0    row = []    seat = []     while count != rows:        row.append('-')       count += 1    counter = 0     while counter != seats:       seat.append('-')       counter += 1    globalseats.append(row)    globalseats.append(seat)    return globalseats   def theater_list():    x in globalseats[0]:        print(''.join(globalseats[1])       globalseats.append(globalseats[1])    print('\n')   def print_theater():    del globalseats[0]    del globalseats[1]     elem in globalseats:       print(''.join(map(str,elem)))    print('\n')   def sell_seat(row_number,seat_number):     if globalseats[row_number][seat_number] == '#':       return true    else:       globalseats[row_number][seat_number] = '#'       return false 

my code calls functions:

import theater  rows = 10 seats_per_row = 20  local_theater = theater.create(rows,seats_per_row) theater.theater_list() theater.print_theater()  if not theater.sell_seat(3,5):    theater.print_theater()  else:    print('seat has been sold')    theater.print_theater()   # part makes sure same seat can not sold twice  if not theater.sell_seat(3,5):    theater.print_theater()  else:    print('seat has been sold')    theater.print_theater()