Python：错误=类'Foo'没有'bar'成员？

Question

我收到一个错误：

AttributeError：类型对象“ Shop”没有属性“ inventory”

我的课程已设置：

class Shop(object):
    def __init__(self, name, inventory, margin, profit):
        self.name = name 
        self.inventory = inventory
        self.margin = margin
        self.profit = profit


# Initial inventory including 2 of each 6 models available
inventory = 12
# Markup of 20% on all sales
margin = .2
# Revenue minus cost after sale
for bike in bikes.values():
    profit = bike.cost * margin

我想打印库存：

print "Mike's Bikes has {} bikes in stock.".format(Shop.inventory)

但仍然会出现相同的错误。 我可以使用它：

print "Mike's Bikes has %d bikes in stock." % (inventory)

但我试图切换到.format（）

Answer 1

您从未创建过该类的实例 ，因此Shop.__init__()方法也从未运行过。

您的班级没有这样的属性； 您为Shop类定义的唯一属性是__init__方法本身。

创建该类的实例，然后在该实例上查找属性：

# Initial inventory including 2 of each 6 models available
inventory = 12
# Markup of 20% on all sales
margin = .2
# Revenue minus cost after sale
for bike in bikes.values():
    profit = bike.cost * margin

bikeshop = Shop("Mike's Bikes", inventory, margin, profit)
print "Mike's Bikes has {} bikes in stock.".format(bikeshop.inventory)

在使用Shop(....)创建实例时，Python创建了实例，并在该实例上调用了__init__方法。 结果， inventory属性被添加到实例，然后您可以通过bikeshop.inventory访问它。