Comparing two dictionaries and printing key value pair in python

Question

I have two dictionaries:

a= { "fruits": ["apple", "banana"] }
b = { "fruits": ["apple", "carrot"]}

Now I want to print the differences. And I want to In this case the output should be

{'fruits' : 'carrot'}

also if the keys have changed - suppose if has changed to

b = { "toy": "car"}

then the output should be

{ "toy": "car"}

Thanks in advance.

You can't actually have those dictionaries. Dictionaries don't work like that. — user2357112, Feb 25 '14 at 04:54
Do you want `'vegetables'` to be printed as well since it's a key in `a` not present in `b`? — jayelm, Feb 25 '14 at 04:55
this is not valid `a = { 'fruits': 'apple' 'grape', 'vegetables': 'carrot'}` — James Sapam, Feb 25 '14 at 04:55
@yopy, *technically* it's "valid", but it's probably not what OP intended :) — mhlester, Feb 25 '14 at 04:56
@yopy two adjacent string literals concatenate, so `'fruits': 'apple' 'grape'` is just `'fruits': 'applegrape'` — Adam Smith, Feb 25 '14 at 05:00

score 3 · Accepted Answer · answered Feb 25 '14 at 05:02

It seems like dict.viewitems might be a good method to look at. This will allow us to easily see which key/value pairs are in a that aren't in b:

>>> a = { 'fruits': 'apple' 'grape', 'vegetables': 'carrot'}
>>> b = { 'fruits': 'banana'}
>>> a.viewitems() - b.viewitems()  # python3.x -- Just use `items` :)
set([('fruits', 'applegrape'), ('vegetables', 'carrot')])
>>> b['vegetables'] = 'carrot'  # add the correct vegetable to `b` and try again.
>>> a.viewitems() - b.viewitems()
set([('fruits', 'applegrape')])

We can even get a handle on what the difference actually is if we use the symmetric difference:

>>> a.viewitems() ^ b.viewitems()
set([('fruits', 'applegrape'), ('fruits', 'banana')])

You could also do something similar with viewkeys (keys on python3.x) if you're only interested in which keys changed.

Thanks a lot ! viewitems was much of help to me :) – user3349548 Feb 28 '14 at 06:22 — user3349548, Feb 28 '14 at 06:22

score 1 · Answer 2 · answered Feb 25 '14 at 05:00

As to the differences, You can use a dictionary comprehension to filter only b keys which are in a:

>>> {key: b[key] for key in b if key in a}
{'fruits': 'banana'}

To the second part, "if the keys have changed", {'froot'} isn't a valid dictionary, and keys are immutable. So it's not possible.

Comparing two dictionaries and printing key value pair in python

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