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.