Python：错误=类'Foo'没有'bar'成员？

Question

I am receiving an error:

AttributeError: type object 'Shop' has no attribute 'inventory'

my class is set:

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

and I want to print inventory:

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

but keep getting the same error. I can make it work with:

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

but am trying to make the switch to .format()

Answer 1

You never created an instance of the class, so the Shop.__init__() method was never run either.

Your class doesn't have such an attribute; the only attribute you defined for your Shop class is the __init__ method itself.

Create an instance of the class, then look for the attribute on that instance:

# 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)

In creating the instance with Shop(....) , Python created the instance and called the __init__ method on that instance. As a result, the inventory attribute was added to the instance, and you can then access it via bikeshop.inventory .