Beginner Python: AttributeError: 'list' object has no attribute

Question

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?

Answer 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.