Receiving an IndexError when the range in the list should not be out of bounds - index-error

Question

I'm new to programming and I can't figure out why I'm getting this error. This is a snippet of code for my battleship script. What I'm trying to do is have a function select spots that are empty to place ships. I've imported random and I have mostly reused this code from my function on setting up the player's ships, which does work. Every once in a while I do not get this error and the game loop progresses as normal. I apologize if I have not given enough information and will update with more and provide full code if you wish to see it. Thank you for looking.
row_headers = ['A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J']
column_headers = [' ', '1', '2', '3', '4', '5', '6', '7', '8', '9', '10']
rows = columns = 10
grid_enemy = []
for row in range(row):
grid_enemy.append([])
for column in range(columns):
grid_enemy[row].append('.')
def setup_ship_enemy(ship_enemy):
random_coordinate = []
random_coordinate.append(random.randint(1,10))
random_coordinate.append(random.randint(1,10))
random_direction = random.randint(1,4) #direction is: UP DOWN LEFT RIGHT
valid_spot_e = 0
for unit_e in range(ship_enemy.size):
if random_direction == 1:
spot_e = -unit_e + -1 + random_coordinate[0]
if spot_e < 0:
return False
elif grid_enemy[spot_e][-1 + random_coordinate[1]] != '.':
return False
else:
valid_spot_e += 1
if valid_spot_e == ship.size:
for unit_e in range(ship_enemy.size):
ship_enemy.position.append([random_coordinate[0] + -unit_e, random_coordinate[1]])
if random_direction == 2:
spot_e = unit_e + -1 + random_coordinate[0]
if spot_e >= 10:
return False
elif grid_enemy[spot_e][-1 + random_coordinate[1]] != '.':
return False
else:
valid_spot_e += 1
if valid_spot_e == ship_enemy.size:
for unit_e in range(ship_enemy.size):
ship_enemy.position.append([random_coordinate[0] + unit_e, random_coordinate[1]])
if random_direction == 3:
spot_e = -unit_e + -1 + random_coordinate[1]
if spot_e < 0:
return False
elif grid_enemy[-1 + random_coordinate[0]][spot_e] != '.':
return False
else:
valid_spot_e += 1
if valid_spot_e == ship_enemy.size:
for unit_e in range(ship_enemy.size):
ship_enemy.position.append([random_coordinate[0], random_coordinate[1] -unit_e])
if random_direction == 4:
spot_e = unit_e + -1 + random_coordinate[1]
if spot_e >= 10:
return False
elif grid_enemy[-1 + random_coordinate[0]][spot_e] != '.':
return False
else:
valid_spot_e += 1
if valid_spot_e == ship_enemy.size:
for unit_e in range(ship_enemy.size):
ship_enemy.position.append([random_coordinate[0], random_coordinate[1] + unit_e])