How to merge dictionaries by combining values ​​by key into a list?

Question

Python

There are many dictionaries:

x = {'a': 1, 'b': 2}
y = {'b': 3, 'c': 4}

}
There is a function
z = x.update(y)
but it overwrites the value by key, and I need a list of values ​​by key in the combined dictionary, i.e.:
z = {'a': 1, 'b': [2.3] , 'c': 4]

Answer 1

You can do this if you do not need to take into account the fact that the value of the source dictionaries may contain lists that cannot be combined into one:

def merge_dicts(*dicts):
    result = {}
    for d in dicts:
        for k,v in d.items():
            if k in result:
                if not isinstance(result[k], list):
                    result[k], t = list(), result[k]
                    result[k].append(t)
                result[k].append(v)
            else:
                result[k] = v
    return result


z = merge_dicts(x, y)