如何在python中组合字典

Question

I have 2 dictionaries

dict1 = {'color': {'attri': ['Black']}, 'diameter': {'attri': ['(300, 600)']}}

dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

I want to combine the 2 dictionaries such that

dict3 = {'color': {'op': 'in', 'attri': ['Black']}, 'diameter': {'op': 'range', 'attri': ['(300,600)']}}

Answer 1

This method uses a defaultdict and is safe even if a key only appears in one of the dictionaries.

import itertools
import collections

dict3 = collections.defaultdict(dict)

for key, value in itertools.chain(dict1.items(), dict2.items()):
     dict3[key].update(value)

---

Proof -- applied to:

dict1 = {'color': {'attri':['Black']}, 'diameter': {'attri':['(300, 600)']}}
dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

the output of dict(dict3) is:

{'color': {'attri': ['Black'], 'op': 'in'},
'diameter': {'attri': ['(300, 600)'], 'op': 'range'},
'size': {'op': 'in'}}

---

Although looking at your expected output, you only want a result if the key appears in both dictionaries, in which case I'd do:

for key in set(itertools.chain(dict1, dict2)):
    if key in dict1 and key in dict2:
         dict3[key] = {**dict1, **dict2}

Answer 2

Just use a mix of dict comprehensions and dict unpacking :

dict1 = {'color': {'attri':['Black']}, 'diameter': {'attri':['(300, 600)']}}
dict2 = {'size': {'op':'in'}, 'diameter': {'op':'range'}, 'color': {'op':'in'}}

dict3 = {n:{**dict1[n],**dict2[n]} for n in dict1}

Answer 3

res = {}
for item in dict1:
  res.setdefault(item, {})
  res[item].update(dict1[item])
  if item in dict2:
    res[item].update(dict2[item])

Answer 4

For dictionaries x and y, z becomes a merged dictionary with values from y and from x.

In Python 3.5 or greater, :

z = {**x, **y}

In Python 2, (or 3.4 or lower) write a function:

def merge_two_dicts(x, y):
    z = x.copy()   # start with x's keys and values
    z.update(y)    # modifies z with y's keys and values & returns None
    return z
and

z = merge_two_dicts(x, y)