Chaining python dictionaries to make a new one

user_459222 0
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I have two python dictionaries, say,

d1 = {'k1':'v1', 'k2':'v2', 'k3':'v3'}
d2 = {'v1':'w1','v2':'w2','v5':'w5'}

what I need is a merged dict like this -

mergeDict= {k1:(v1,w1), k2:(v2,w2), k3:(v3)}

Whatever I have been able to look up or read has dealt with appending dictionaries, nothing like this. I called this chaining since value of first dict is potentially the key in second dict.

So far i have done this through typical loop and lookup on keys(). Wondering if there is a more pythonic way to achieve this that i might be missing here ?

dictionary python
3 Answers

A dict comprehension seems to work:

out = {k: (v, d2[v]) if v in d2 else (v,) for k,v in d1.items()}

Output:

{'k1': ('v1', 'w1'), 'k2': ('v2', 'w2'), 'k3': ('v3',)}
Admin1

If you meant to merge values with the same key into a collection, you could

  • create a new dict
  • use itertools to iterate over any number of dicts
  • some default value you can pack into (such as a list or set)
import itertools

d3 = {}
for key, value in itertools.chain(d1.items(), d2.items()):
    d3.get(key)
    try:
        d3[key].append(value)  # add value to list
    except KeyError:           # first instance of key
        d3[key] = [value]      # start a fresh list

Note, this doesn't meet the question as-written, which is trying to pack keys matching the same value in another dict, but share the keys between 'em

>>> d1 = {"k1":"v1","k2":"v2","k3":"v3"}
>>> d2 = {"v1":"w1","v2":"w2","v5":"w5"}
[..]
>>> d3
{'k1': ['v1'], 'k2': ['v2'], 'k3': ['v3'], 'v1': ['w1'], 'v2': ['w2'], 'v5': ['w5']}
user_45410450

You can use sets and dict update with Python 3.9+

>>> {k:(d1[k],) for k in d1} | {k:(d1[k],d2[k]) for k in set(d1) & set(d2)} 
{'k1': ('v1', 'w1'), 'k2': ('v2', 'w2'), 'k3': ('v3',)}
user_2986070
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