CODEWITHSUNDEEP
python
tusky
tusky

Reputation: 37

How do I count the items on a "grocery list" using a class?

I am trying to make a class that includes the ability to display the length of a list. However, I get the message 'List has 0 items' instead of the actual number.

Here is my code:

'''

    grocery_list = []
    class GroceryList:
        grocery_list = []
        def __init__(self):
            print('Grocery List Created')
        def add(self, item):
            self.grocery_list.append(item)
        def show(self):
    print(self.grocery_list)
        def size(self):
             print('List has {} items'.format(len(grocery_list)))


    gro_list = GroceryList()
    gro_list.add('Banana')
    gro_list.add('Cat Food')
    gro_list.show()
    gro_list.size()

'''

Any help is appreciated.

Upvotes: 1

Views: 262

Answers (3)

Ram
Ram

Reputation: 4779

  • You have two grocery_list in your code. One is a global one and the other is a class variable.
  • By len(grocery_list) You are finding the length of the grocery_list that is declared before the Class (global). Since you're not adding to that list (see your add() function), it shows you 0 items.
  • It should be len(self.grocery_list) - means find the length of grocery_list (class variable). See the self before the variable name.
class GroceryList:
    grocery_list = []
    def __init__(self):
        print('Grocery List Created')
    def add(self, item):
        self.grocery_list.append(item)
    def show(self):
        print(self.grocery_list)
    def size(self):
        print('List has {} items'.format(len(self.grocery_list)))


gro_list = GroceryList()
gro_list.add('Banana')
gro_list.add('Cat Food')
gro_list.show()
gro_list.size()

Grocery List Created
['Banana', 'Cat Food']
List has 2 items

Upvotes: 1

Derek
Derek

Reputation: 2244

In your question the indentation was messed up, however the problem was in method size(self) with grocery_list used instead of self.grocery_list.

Everything else works OK.


class GroceryList:

    # declare grocery_list
    grocery_list = []

    def __init__(self):
        print('Grocery List Created')

    def add(self, item):
        self.grocery_list.append(item)

    def show(self):
        print(self.grocery_list)

    def size(self):
        # self.grocery_list was the error
        print('List has {} items'.format(len(self.grocery_list)))

if __name__ == "__main__":

    gro_list = GroceryList()
    gro_list.add('Banana')
    gro_list.add('Cat Food')
    gro_list.show()
    gro_list.size()

Upvotes: 1

PCM
PCM

Reputation: 3011

The reason you get zero in your code is that you are appending to the list (grocery_list) which is an attribute of the class. But in the size() function you are printing the length of the global grocery_list in which no elements were appended (i.e it is an empty list) so you get length as '0'

Try changing your size() function to this -

def size(self):
    print('List has {} items'.format(len(self.grocery_list)))

Also, you can remove the grocery_list variable at the global level (first line), because it is useless in this code.

Upvotes: 0

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