How can I merge two Python dictionaries additive?

Question

I want to merge two Python dictionaries additive, like this:

 a = {'result': {'sessionId': '111'}}
 b = {'result': {'completelyOtherSessionId': '100'}}
 ##magic##
 c = {'result': {'sessionId': '111', 'completelyOtherSessionId': '100'}}

Asked By: knurzl

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Source

Answer 1

>>> a = {'result': {'sessionId': '111'}}
>>> b = {'result': {'sessionsId': '100'}}
>>> с = a.copy()
>>> for key in c:
>>>     c[key].update(b[key])
>>> print(c)
{'result': {'sessionId': '111', 'sessionsId': '100'}}

Please understand that this solution only works for your specific case (a and b‘s values are also dictionaries). Otherwise the update method would not be available and you’d get an AttributeError exception.

Answered By: arrakis_sun

Answer 2

Here’s a Python2/3 function that will not alter the dicts you give it. It will create a new one and attempt to combine them all. Keep in mind that it doesn’t handle collisions in any advanced way. It simply overwrites it with the right-most dict parameter.

def add_dicts(*dicts):
    ret, dicts = dict(), list(dicts)
    dicts.insert(0, ret)
    try:
        red = reduce
    except NameError:
        red = __import__("functools").reduce
    red(lambda x, y: x.update(y) or x, dicts)
    return ret

Example:

a = {"a": 1}
b = {"b": 2}
c = {"c": 3}

var = add_dicts(a, b, c)
print(a)  # => {"a": 1}
print(b)  # => {"b": 2}
print(c)  # => {"c": 3}
print(var)  # => {'a': 1, 'c': 3, 'b': 2}

Answered By: Goodies

How can I merge two Python dictionaries additive?

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