问题
The error says:
AttributeError: 'list' object has no attribute 'cost'
I am trying to get a simple profit calculation to work using the following class to handle a dictionary of bicycles:
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]
}
When I try to calculate profit with my for statement, I get the attribute error.
# Markup of 20% on all sales
margin = .2
# Revenue minus cost after sale
for bike in bikes.values():
profit = bike.cost * margin
First, I don't know why it is referring to a list, and everything seems to be defined, no?
回答1:
Consider:
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)
Output:
33.0 20.0
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'
this will occur when you try to call .cost
on a list
object. Pretty straightforward, but we can figure out what happened by looking at where you call .cost
-- in this line:
profit = bike.cost * margin
This indicates that at least one bike
(that is, a member of bikes.values()
is a list). If you look at where you defined bikes
you can see that the values were, in fact, lists. So this error makes sense.
But since your class has a cost attribute, it looked like you were trying to use Bike
instances as values, so I made that little change:
[...] -> Bike(...)
and you're all set.
回答2:
They are lists because you type them as lists in the dictionary:
bikes = {
# Bike designed for children"
"Trike": ["Trike", 20, 100],
# Bike designed for everyone"
"Kruzer": ["Kruzer", 50, 165]
}
You should use the bike-class instead:
bikes = {
# Bike designed for children"
"Trike": Bike("Trike", 20, 100),
# Bike designed for everyone"
"Kruzer": Bike("Kruzer", 50, 165)
}
This will allow you to get the cost of the bikes with bike.cost as you were trying to.
for bike in bikes.values():
profit = bike.cost * margin
print(bike.name + " : " + str(profit))
This will now print:
Kruzer : 33.0
Trike : 20.0
回答3:
You need to pass the values of the dict into the Bike
constructor before using like that. Or, see the namedtuple
-- seems more in line with what you're trying to do.
来源:https://stackoverflow.com/questions/29335423/beginner-python-attributeerror-list-object-has-no-attribute