python - 初学者 Python : AttributeError: 'list' object has no attribute

Question

错误说:

AttributeError: 'list' object has no attribute 'cost' 

我正在尝试使用以下类处理自行车字典来进行简单的利润计算:

class Bike(object):
    def __init__(self, name, weight, cost):
        self.name = name
        self.weight = weight
        self.cost = cost

bikes = {
    # Bike designed for children"
    "Trike": ["Trike", 20, 100],
    # Bike designed for everyone"
    "Kruzer": ["Kruzer", 50, 165]
    }

当我尝试使用我的 for 语句计算利润时，出现属性错误。

# Markup of 20% on all sales
margin = .2
# Revenue minus cost after sale
for bike in bikes.values():
    profit = bike.cost * margin

首先，我不知道为什么它指的是一个列表，而且一切似乎都被定义了，不是吗？

Answer 1

考虑:

class Bike(object):
    def __init__(self, name, weight, cost):
        self.name = name
        self.weight = weight
        self.cost = cost

bikes = {
    # Bike designed for children"
    "Trike": Bike("Trike", 20, 100),      # <--
    # Bike designed for everyone"
    "Kruzer": Bike("Kruzer", 50, 165),    # <--
    }

# Markup of 20% on all sales
margin = .2
# Revenue minus cost after sale
for bike in bikes.values():
    profit = bike.cost * margin
    print(profit)

输出:

33.020.0

The difference is that in your bikes dictionary, you're initializing the values as lists [...]. Instead, it looks like the rest of your code wants Bike instances. So create Bike instances: Bike(...).

As for your error

AttributeError: 'list' object has no attribute 'cost'

当您尝试在 list 对象上调用 .cost 时会发生这种情况。非常简单，但我们可以通过查看调用 .cost 的位置来弄清楚发生了什么——在这一行中:

profit = bike.cost * margin

这表示至少有一个bike(即bikes.values()的成员是一个列表)。如果查看定义 bikes 的位置，您会发现这些值实际上是列表。所以这个错误是有道理的。

但是由于你的类有一个成本属性，看起来你正试图使用​​ Bike 实例作为值，所以我做了一点改变:

[...] -> Bike(...)

一切就绪。