Question

简介：我正在尝试将购物清单代码放在一起。但是，每次我输入一个项目而不是将其存储在列表中时，我都会收到一条错误消息，指出未定义该项目。

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()

问题：为什么不将字符串存储到列表中？

Answer 1

这是正确的，因为您没有将任何项目传递给add_to_list()方法。

代码应类似于：

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() 解释，例如，如果用户是输入一个整数值，输入函数将返回该整数值。另一方面，如果用户输入列表，则该函数将返回列表。

如果您不将输入内容括在引号中，Python会将您的姓名作为变量。因此，错误消息很有意义！

为避免此错误，您必须将变量 input 转换为字符串。例如：“ ABC”

或者，您可以使用raw_input()。 raw_input 不解释 。它总是返回用户的输入而未更改，即原始。可以将原始输入更改为算法所需的数据类型。

Further Reading

Answer 3

您还误解了功能show_list。这是在Python 3.7上进行的测试

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

根据给出的错误，我认为您可能正在使用Python 2.7，并且该错误是因为您使用的是input()而不是raw_input()。使用Python 3时，应使用input()。

因此，将new_item = input("> ")更改为new_item = raw_input("> ")，这应该会停止您的错误。

但是，您的代码中也存在错误，您在show_list函数中也打印了最终列表。除非您调用enumerate，否则for循环只会遍历列表中的每个项目，除非它会循环遍历返回索引和项目。

这可能是您在该功能中需要的：

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

Python：购物清单：不存储的商品

4 个答案: