Merging 2 dictionaries in python

Question

I have two dictionary:

a=

{
    "2001935072": {
        "WR": "48.9",
        "nickname": "rogs30541",
        "team": 2
    },
....
}

and

b=

{
    "2001935072": {
        "wtr": 816
    },
....
}

i've tried to merge them with both a.update(b) and a={**a, **b} but both gives this output when i print(a):

{
    "2001935072": {
        "wtr": 816
    },
....
}

which is basicly a=b, how to merge A and B so the output is

{
    "2001935072": {
        "WR": "48.9",
        "nickname": "rogs30541",
        "team": 2
        "wtr": 816
    },
....
}

Possible duplicate of [How to merge two dictionaries in a single expression?](https://stackoverflow.com/questions/38987/how-to-merge-two-dictionaries-in-a-single-expression) — Jongware, Feb 07 '18 at 09:44
What should the rule for conflicting keys be. Meaning, which value should be taken if let's say `a["2001935072"]["WR"]=48.9` and `b["2001935072"]["WR"]=50`? — FlyingTeller, Feb 07 '18 at 09:46
Loop the keys and merge them each, as you hold a dict of dicts, and `update` isn't recursive. Something like `{key: a[key].update(value) for key, value in b.iteritems()}` — casraf, Feb 07 '18 at 09:48
@FlyingTeller there wont be any conflicting keys because b will only contain "wtr" and nothing else — Yosua Sofyan, Feb 07 '18 at 09:49
@casraf i thought about that but asked here because i think theres more simple way to do it :( . Alright then ill do just that thx man — Yosua Sofyan, Feb 07 '18 at 09:55

Jean-François Fabre · Answer 1 · 2018-02-07T10:34:51.690

I would compute the union of the keys, then rebuild the dictionary merging the inner dictionaries together with an helper method (because dict merging is possible in 3.6+ inline but not before) (How to merge two dictionaries in a single expression?)

a={
    "2001935072": {
        "WR": "48.9",
        "nickname": "rogs30541",
        "team": 2
    }
    }
b= {
    "2001935072": {
        "wtr": 816
    },

}
def merge_two_dicts(x, y):
    """Given two dicts, merge them into a new dict as a shallow copy."""
    z = x.copy()
    z.update(y)
    return z

result = {k:merge_two_dicts(a.get(k,{}),b.get(k,{})) for k in set(a)|set(b)}

print(result)

result:

{'2001935072': {'WR': '48.9', 'nickname': 'rogs30541', 'team': 2, 'wtr': 816}}

notes:

a.get(k,{}) allows to get the value for k with a default of so merge still works, only retaining values from b dict.
merge_two_dicts is just an helper function. Not to be used with a and b dicts directly or it will give the wrong result, since last merged one "wins" and overwrites the other dict values

With Python 3.6+: you can do that without any helper function:

result = {k:{**a.get(k,{}),**b.get(k,{})} for k in set(a)|set(b)}

works perfectly on my machine. what is the error? I don't have access to replit. — Jean-François Fabre, Feb 07 '18 at 10:27
when i run merge_two_dicts(a, b) the result is { "2001935072": { "wtr": 816 } } — Yosua Sofyan, Feb 07 '18 at 10:30

score 1 · Accepted Answer · answered Feb 07 '18 at 09:56

1

Try this:-

for i,j in a.items():
    for x,y in b.items():
        if i==x:
            j.update(y)

print(a) #your updateed output

answered Feb 07 '18 at 09:56

Narendra

1,511
1
10
20

that's very bad complexity-wise: useless `O(n**2)` – Jean-François Fabre Feb 07 '18 at 10:40

score 1 · Answer 3 · answered Feb 07 '18 at 10:29

You can try list + dict comprehension to achieve your results:

>>> a = {"2001935072":{"WR":"48.9","nickname":"rogs30541","team":2}}
>>> b = {"2001935072":{"wtr":816}}
>>> l = dict([(k,a.get(k),b.get(k)) for k in set(list(a.keys()) + list(b.keys()))])

This will output:

>>> [('2001935072', {'WR': '48.9', 'nickname': 'rogs30541', 'team': 2}, {'wtr': 816})]

Finally to achieve your desired output

>>> dict((k,{**va,**vb}) for k,va,vb in l)
>>> {'2001935072': {'WR': '48.9', 'nickname': 'rogs30541', 'team': 2, 'wtr': 816}}

Merging 2 dictionaries in python

3 Answers3