How can 2 Python dictionaries become 1?

Question

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Python “extend” for a dictionary

I know that Python list can be appended or extended. Is there an easy way to combine two Python dictionaries with unique keys, for instance:

basket_one = {'fruit': 'watermelon', 'veggie': 'pumpkin'}
basket_two = {'dairy': 'cheese', 'meat': 'turkey'}

I then want one big basket of food:

basket = {
    'fruit': 'watermelon', 
    'veggie': 'pumpkin', 
    'dairy': 'cheese', 
    'meat': 'turkey'
}

How can I perform the above in Python?

score 65 · Accepted Answer · edited Jun 07 '19 at 18:19

65

The "oneliner way", altering neither of the input dicts, is

basket = dict(basket_one, **basket_two)

In case of conflict, the items from basket_two will override the ones from basket_one. As one-liners go, this is pretty readable and transparent, and I have no compunction against using it any time a dict that's a mix of two others comes in handy (any reader who has trouble understanding it will in fact be very well served by the way this prompts him or hear towards learning about dict and the ** form;-). So, for example, uses like:

x = mungesomedict(dict(adict, **anotherdict))

are reasonably frequent occurrences in my code.

Note: In Python 3, this will only work if every key in anotherdict is a string. See these alternatives.

edited Jun 07 '19 at 18:19

pianoJames

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answered Oct 11 '09 at 21:47

Alex Martelli

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This is fairly common, a good idiom that everyone should know – John La Rooy Oct 11 '09 at 21:58
Wow, that's a really interesting way of combining 2 dictionaries. It uses basic Python. I'm glad this answer has been sneaked in before the question has closed. – Thierry Lam Oct 12 '09 at 02:21

score 9 · Answer 2 · answered Oct 11 '09 at 20:29

9

basket = basket_one.copy()
basket.update(basket_two)

(if the original basket_one does not need to stay intact, you can leave out the copy)

answered Oct 11 '09 at 20:29

sepp2k

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How can 2 Python dictionaries become 1?

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