NameError: Variable name is not defined

Question

I am having trouble with some undefined variables in my code for a school assignment using nested loops and functions. Also, if you happen to spot any other errors please lmk.

Code:

shopping_lists = [
['toothpaste', 'q-tips', 'milk'],
['milk', 'candy', 'apples'],
['planner', 'pencils', 'q-tips']
]

customer_input = ''

#prints shopping lists
print(shopping_lists)
print ('')

print("Press '1' to update an item, '2' to view an item, or '3' to view a list")
customer_input = input("What do you want to do? ")
if customer_input == '1':
  def update_list(List, Item, newItem):
    list = int(input('What list would you like to update? Answer using 1, 2, or 3. ')-1)
    print (shopping_lists[list])
    
    itm = int(input('What item would you like to view? ')-1)
    print (shopping_lists[list][itm])
    
    newItm = input('What would you like to change the item to? ')
    shopping_lists[list][itm] = newItm
    
    update_list(list, itm, newItm)

def view_item():
  pass

def view_list():
  pass

#While loop
while 'stop' not in customer_input:
  update_list(list, itm, newItm)

Answer 1

I would rearrange your execution flow as follows.

shopping_lists = [
    ['toothpaste', 'q-tips', 'milk'],
    ['milk', 'candy', 'apples'],
    ['planner', 'pencils', 'q-tips']
]

def handle_action(action):
    if action == '1':
        update_list()
    elif action == '2':
        view_item()
    elif action == '3':
        view_list() 
    else:
        pass
        # What if an unrecognized action is used?

def update_list():
    list_number = int(input('What list would you like to update? Answer using 1, 2, or 3. ')) - 1
    print(shopping_lists[list_number])
    
    itm = int(input('What item would you like to view? ')) - 1
    print(shopping_lists[list_number][itm])
    
    newItm = input('What would you like to change the item to? ')
    shopping_lists[list_number][itm] = newItm

    
def view_item():
    pass


def view_list():
    pass


#While loop
customer_input = ''
while customer_input != 'stop':
    print(shopping_lists)
    print("Press 1 to update an item, 2 to view an item, or 3 to view a list")
    customer_input = input("What do you want to do? ")
    handle_action(customer_input)

Notice the difference on the usage of stop as a break word for the loop. And the handle_action function to control a switch of what you are doing.

I also renamed list to list_number because list is a type name in python.