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pythonpython-3.xdictionarymerge

How to unpack or merge a variadic list of dictionaries in Python?


According to this answer, in Python 3.5 or greater, it is possible to merge two dictionaries x and y by unpacking them:

z = {**x, **y}

Is it possible to unpack a variadic list of dictionaries?

Something like

def merge(*dicts):
    return {***dicts} # this fails, of course. What should I use here?

For instance, I would expect that

list_of_dicts = [{'a': 1, 'b': 2}, {'c': 3}, {'d': 4}]
{***list_of_dicts} == {'a': 1, 'b': 2, 'c': 3, 'd': 4}

Note that this question is not about how to merge lists of dictionaries since the link above provides an answer to this. The question here is: is it possible, and how, to unpack lists of dictionaries?

As stated in the comments, this question is very similar to this one. However, unpacking a list of dictionaries is different from simply merging them. Supposing that there was an operator *** designed to unpack lists of dictionaries, and given

def print_values(a, b, c, d):
    print('a =', a)
    print('b =', b)
    print('c =', c)
    print('d =', d)

list_of_dicts = [{'a': 1, 'b': 2}, {'c': 3}, {'d': 4}]

it would be possible to write

print_values(***list_of_dicts)

instead of

print_values(**merge(list_of_dicts))

Solution

  • Another solution is using collections.ChainMap

    from collections import ChainMap
    
    dict(ChainMap(*list_of_dicts[::-1]))
    
    Out[88]: {'a': 1, 'b': 2, 'c': 3, 'd': 4}