Python iterating through lists and dictionaries

Question

This is a test project from a python book. I am trying to iterate through a list and check if each item is a key in the dictionary. If it is, then add 1 to the dictionary value, if not add the key and then set the value to 1. Here's my code so far:

inv_original = {'gold coin' : 42, 'rope' : 1}
dragonloot = ['gold coin', 'dagger', 'gold coin', 'gold coin', 'ruby']

def addtoinventory(dict_a, addeditems):
    for i in addeditems:
        if dict_a.has_key(i):
            dict_a[str(i)] = dict_a.get(i, 0) + 1
        else:
            dict_a[str(i)] = 1
        return dict_a

    inv = addtoinventory(inv_original, dragonloot)

    print inv

It seems to work but only for the first item in the list, it doesn't iterate through the rest. Can anyone help please?

Answer 1

Your function returns after completing the first iteration.

def addtoinventory(dict_a, addeditems):
    for i in addeditems:
        if dict_a.has_key(i):
            dict_a[str(i)] = dict_a.get(i, 0) + 1
        else:
            dict_a[str(i)] = 1
        return dict_a     # <----- issue here
# ...

You should move the return statement outside the loop's body by unindenting the line by 4 spaces to fix the issue. You should also consider:

• using a try/except block instead of if/else,
• removing the str(i) call; your list elements are already strings, so it's unnecessary to attempt a string conversion on them, and
• improved variable names (e.g. inventory instead of dict_a, and items instead of addeditems, which is likely redundant --if it's in the list, it has obviously been added :)

The updated code is below:

#!/usr/bin/python

inv_original = {'gold coin' : 42, 'rope' : 1}
dragonloot   = ['gold coin', 'dagger', 'gold coin', 'gold coin', 'ruby']

def addtoinventory(inventory, items):
    for i in items:
        try:
            inventory[i] += 1
        except KeyError:
            inventory[i] = 1

    return inventory

#
print addtoinventory(inv_original, dragonloot)
# ...

The code's output is now: {'gold coin': 45, 'rope': 1, 'dagger': 1, 'ruby': 1}, showing that the gold coin key has increased by 3 and other key/val pairs have been added, as you expected.