Python - Class variables vs dictionary of values

Question

Lets say I've got a class which represents an object that has many properties (simple data types like strings and integers). Should they be represented as instance variables or would the better "pythonic" be to put them into a dictionary?

For example:

class FruitBasket:
    def __init__(self,apples, oranges, bananas, pears): #number of apples, oranges etc...
        self.apples = apples
        self.oranges = oranges
        self.bananas = bananas
        self.pears = pears



class FruitBasket:
    def __init__(self, fruits): #fruits is a dictionary
        self.fruits = fruits

Answer 1

My general philosophy is to use attributes if the set of items is more or less fixed, and use a dictionary if the set may change on an ad-hoc basis. If your FruitBasket is specifically made to contain apples, oranges, bananas and pears, then use attributes. If it may contain any random assortment of other things (e.g., you might sometimes throw in a pineapple or a raspberry), use a dictionary.

One reason can be sort of seem even in your example code. If you use attributes, you have to specify each one literally in the code (e.g., self.pears). Moreover, you often wind up doing what you did here, where you explicitly pass each item as an argument to __init__. This obviously won't work if you later decide to add new fruits. You could keep adding more arguments to __init__, but that quickly becomes unwieldy.

In addition, if you have a fixed set of items, you'll probably be accessing them individually. That is, if you know you only have apples, oranges, bananas, and pears, you can directly access them by name as you did here (self.apples, self.oranges, etc.). If you don't know ahead of time what fruits may be in the basket, you can't know what names to use a prior, so you'll typically process them by iterating over them. It is very easy to iterate over the items of a dictionary. By contrast, iterating over the attributes of an object is fraught with peril, since you can't easily distinguish the attributes that contain data that the object is "about" (e.g., self.pears) from those that pertain to the structure of the object itself (e.g., self.__init__, self.basketColor, self.basketSize, etc.).

In short, if you don't know ahead of time what will be in the basket, you'll want to iterate over its contents, and if you want to iterate over something's contents, it's best to use a type designed for containment (like a list or dict), because these types cleanly separate the container from its contents.