CODEWITHSUNDEEP
pythondictionarykeyerror
user2455916
user2455916

Reputation:

KeyError iterating through keys in a list

Hi all so I wrote a function which is something like this 

def solve_one_shop(shop, items):
    if len(items) == 0:
        return [0.0, []]
    all_possible = []
    first_item = items[0]
    print shop['burger']
    for (price,combo) in shop[first_item]:
        # DO SOMETHING
        #

solver(shop_text,['burger'])

The dictionary that Im trying to iterate over is this :

{'1': {'burger': [[4.0, ['burger']]], 'tofu_log': [[8.0, ['tofu_log']]]}, '3': {'chef_salad': [[4.0, ['chef_salad']]], 'steak_salad_sandwich': [[8.0, ['steak_salad_sandwich']]]}, '2': {'burger': [[5.0, ['burger']]], 'tofu_log': [[6.5, ['tofu_log']]]}, '5': {'extreme_fajita': [[4.0, ['extreme_fajita']]], 'fancy_european_water': [[8.0, ['fancy_european_water']]]}, '4': {'wine_spritzer': [[2.5, ['wine_spritzer']]], 'steak_salad_sandwich': [[5.0, ['steak_salad_sandwich']]]}, '6': {'extra_salsa': [[6.0, ['extreme_fajita', 'jalapeno_poppers', 'extra_salsa']]], 'jalapeno_poppers': [[6.0, ['extreme_fajita', 'jalapeno_poppers', 'extra_salsa']]], 'extreme_fajita': [[6.0, ['extreme_fajita', 'jalapeno_poppers', 'extra_salsa']]], 'fancy_european_water': [[5.0, ['fancy_european_water']]]}}

The problem is that the 6th line is giving KeyError ( shop[first_item] ).

[[4.0, ['burger']]]
Traceback (most recent call last):
  File "working.py", line 58, in <module>
    solver(shop_text,['burger'])
  File "working.py", line 44, in solver
    (price, solution) = solve_one_shop(shop_info, required_items)
  File "working.py", line 29, in solve_one_shop
    for (price,combo) in shop.get(first_item):
TypeError: 'NoneType' object is not iterable

To overcome this error I tried hardcoding, so for example if I hardcode the first_item as shop['burger'] (along with single quotes), then the code runs.

But if I write it as shop[burger] , then it throws the same KeyError: 'burger'

As you can see , print shop['burger'] outputs the availability of the key 'burger', but then why the KeyError.

How to fix this?

Upvotes: 0

Views: 13018

Answers (2)

Srikar Appalaraju
Srikar Appalaraju

Reputation: 73588

You are trying to access a key from the dict (here shop), which is not present. Hence the error. Check if that key first_item is present in your dict. You would not get this error (updated answer).

...
if first_item in shop:
    for (price,combo) in shop[first_item]:
        ...

or use try: except:

   ...
    try:
        for (price,combo) in shop[first_item]:
    except KeyError: 
        print 'ERROR: key not found!'
    ...

Upvotes: -1

Slater Victoroff
Slater Victoroff

Reputation: 21914

If you want a safer way to access dictionary keys in python I would suggest using the get method. For instance:

shop.get(first_item, False)

Where the second argument is the default return in case the dictionary does not contain the item you are trying to access.

As Jon pointed out, you can also do something like this:

shop.get(first_item, [])

and iteration will stop if your dictionary doesn't contain that key.

Upvotes: 5

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