Question

我刚刚开始学习python，并编写了具有三个功能的脚本。通过Q输入后，我收到一个Traceback错误。

这只是一项学习练习，因此我可以发展自己的Python技能。学习模块的源代码和我的代码似乎完全相同，但是由于某种原因，我的输出返回错误。

 File "C:\Users\Desktop\DearWorld\new.py", line 36, in <module>
    main()
  File "C:\Users\Desktop\DearWorld\new.py", line 33, in main
    total = bill_total(orders, menu)
  File "C:\Users\Desktop\DearWorld\new.py", line 24, in bill_total
    for order in orders:
TypeError: 'NoneType' object is not iterable

menu = {'Angel Dust Blunt': 6.66, 'The OG Blunt': 4.20, 'Caviar Blunt': 7.10, 'The Chronic Blunt' : 4.20}

def print_menu(menu):
    for name, price in menu.items():
        print(name, ': $', format(price, '.2f'), sep = '')

def get_order(menu):        
    orders = []
    order = input("What would you like to order (Q to quit)")

    while (order.upper()  != 'Q'):
    #Find the order and add it to the list if it exists
        found = menu.get(order)
        if found:
            orders.append(order)
        else:
            print("Menu item doesn't exist")

        order = input("Anything else? (Q to Quit)")

def bill_total(orders, menu):
    total = 0

    for order in orders:
        total += menu[order]

    return total

def main():
    menu = {'Angel Dust Blunt': 6.66, 'The OG Blunt': 4.20, 'Caviar Blunt': 7.10, 'The Chronic Blunt' : 4.20}
    print_menu(menu)
    orders = get_order(menu)
    total = bill_total(orders, menu)
    print("You ordered:" ,order, "Your total is: $", format(total, '.2f'), sep='')

main()

The script is supposed to return the bill_total and the items ordered as the output. What is returned instead when the user enters 'Q' is a 'TypeError'

Answer 1

您的get_order函数未返回任何内容，因此该行中orders的值：

orders = get_order(menu)

将为None。然后，您尝试遍历该变量，它将失败。

您需要在get_order函数的末尾添加以下行：

return orders

因此函数应如下所示：

def get_order(menu):        
    orders = []
    order = input("What would you like to order (Q to quit)")

    while (order.upper()  != 'Q'):
    #Find the order and add it to the list if it exists
        found = menu.get(order)
        if found:
            orders.append(order)
        else:
            print("Menu item doesn't exist")

        order = input("Anything else? (Q to Quit)")

    return orders  # Added this line

Answer 2

原因是orders是None，这是因为函数get_order不返回任何内容。

看看这一行：

orders = get_order(menu)

您应该添加：

return orders

在get_order函数末尾

。像这样：

def get_order(menu):        
    orders = []
    order = input("What would you like to order (Q to quit)")

    while (order.upper()  != 'Q'):
    #Find the order and add it to the list if it exists
        found = menu.get(order)
        if found:
            orders.append(order)
        else:
            print("Menu item doesn't exist")

        order = input("Anything else? (Q to Quit)")

    return orders

Answer 3

您的get_order()函数没有return语句。结果，它将始终返回None。因此，在main()中：

orders = get_order(menu)
total = bill_total(orders, menu)

orders将获得一个值None，然后将其传递给bill_total()。当您尝试在for循环中进行迭代时，结果就是您所看到的异常

Answer 4

最新答案，但您可以使用：

// existing unmanaged code
class UnmanagedClass
{
public:
    void SomeMethod();
};

// a C++ CLR
ref class ManagedWrapper
{
public:
    void SomeMethod()
    {
        obj->SomeMethod();
    }

private:
    UnmanagedClass* object;
};

Python Demo
Asciinema（只是为了好玩）

如何解决我的代码中的“ NoneType”错误

4 个答案: