Python：购物清单：不存储的商品

Question

Intro: I am trying to put a shopping list code together. However, every time that I input an item, instead of storing the item in the list, I get a error saying that that item is not defined.

shopping_list = []


def show_help():
    print("What should we pick up at the store?")

    print("""
  Enter 'DONE' to stop adding items.
  Enter 'HELP' for this help.
  Enter 'SHOW' to see your current list.
  """)


def add_to_list():
shopping_list.append(new_item)
print("Here is the item that it's been added {}. There are now {} items".format(new_item, len(shopping_list)))


def show_list():
    index =  1
    for index, item in shopping_list:
        print("Here is the current  shopping list: {}. {}".format(index,item))
    index = index + 1
show_help()

while True:
    new_item = input("> ")

     if new_item == 'DONE':
        break
     elif new_item == 'HELP':
        show_help()
        continue
     elif new_item == 'SHOW':
        show_list()
        continue

     add_to_list()

show_list()

Question: Why is not storing the string into the list?

Answer 1

That is true because you are not passing any item to add_to_list() method.

The code should be like:

shopping_list = []


def show_help():
    print("What should we pick up at the store?")

    print("""
  Enter 'DONE' to stop adding items.
  Enter 'HELP' for this help.
  Enter 'SHOW' to see your current list.
  """)


def add_to_list(new_item):
    shopping_list.append(new_item)
    print("Here is the item that it's been added {}. There are now {} items".format(new_item, len(shopping_list)))


def show_list():
    index =  1
    for index, item in shopping_list:
        print("Here is the current  shopping list: {}. {}".format(index,item))
    index = index + 1
show_help()

while True:
    new_item = input("> ")

     if new_item == 'DONE':
        break
     elif new_item == 'HELP':
        show_help()
        continue
     elif new_item == 'SHOW':
        show_list()
        continue

     add_to_list(new_item)

show_list()

Answer 2

input() interprets the input, ie If the user eg puts in an integer value, the input function returns this integer value. If the user on the other hand inputs a list, the function will return a list.

If you don't wrap your input into quotes, Python takes your name as a variable. So, the error message makes sense!

To avoid this error you have to cast the variable input into a string. eg: "ABC"

---

Alternatively, you can use raw_input() . raw_input does not interpret the input. It always returns the input of the user without changes, ie raw. This raw input can be changed into the data type needed for the algorithm.

Further Reading

Answer 3

you also had the function show_list wrong. This was test on Python 3.7

shopping_list = []

def show_help():
    print("What should we pick up at the store?")

    print("""
  Enter 'DONE' to stop adding items.
  Enter 'HELP' for this help.
  Enter 'SHOW' to see your current list.
  """)


def add_to_list():
    shopping_list.append(new_item)
    print("Here is the item that it's been added {}. There are now {} items".format(new_item, len(shopping_list)))


def show_list():
    for index, item in enumerate(shopping_list):
        print("Here is the current  shopping list: {}. {}".format(index, item))
    show_help()

while True:
    new_item = input("> ")

    if new_item == 'DONE':
        break
    elif new_item == 'HELP':
        show_help()
        continue
    elif new_item == 'SHOW':
        show_list()
        continue

    add_to_list()

show_list()

Answer 4

Based on your error given, I think you might be using Python 2.7 and the error is because you used input() instead of raw_input() . When using Python 3 input() should be used.

So change new_item = input("> ") to be new_item = raw_input("> ") and that should stop your error.

---

However there is also an error in your code where you print out the final list in the show_list function as well. A for loop only goes through each item in teh list unless you call enumerate which will return the index and the item as it loops through.

This is probably what you are looking for in that function:

def show_list():
    for index, item in enumerate(shopping_list):
        print("Here is the current shopping list: {}. {}".format(index,item))