Python: Merge Multilevel dictionaries (append without replace)

Question

I need to merge two dictionaries (multilevel), which are (in a very reduced form) like

 a = {'a' : {'b' : '1'}}
 b = {'a' : {'c' : '2'}}

The result should be

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

Does Python (3.9) provide a function to merge them in the required way? Or can this be done in a failsave procedure?

The actual data has several more levels with different length.

Thanks in advance.

Answer 1

a = {'a' : {'b' : '1'}}
b = {'a' : {'c' : '2'}}

aset = set(a)
bset = set(b)

c=dict()
#first common keys
for name in aset.intersection(bset):
    c[name]=dict(a[name], **b[name])
#keys in a but not in b
for name in aset-bset:
    c[name]=a[name]
#keys in b but not in a
for name in bset-aset:
    c[name]=b[name]
#print fully merged c
print(c)

>>> {'a': {'b': '1', 'c': '2'}}

I used sets to simplify finding common keys etc, you can check this question.

On a more complete example:

a = {'a' : {'b' : '1'},'e':{'l':'2'},'f':{'x':'10'}}
b = {'a' : {'c' : '2'},'e':{'i':'2'},'g':{'z':'12'}}

aset = set(a)
bset = set(b)

c=dict()
for name in aset.intersection(bset):
    c[name]=dict(a[name], **b[name])
for name in aset-bset:
    c[name]=a[name]
for name in bset-aset:
    c[name]=b[name]
print(c)

>>> {'a': {'b': '1', 'c': '2'}, 'e': {'l': '2', 'i': '2'}, 'f': {'x': '10'}, 'g': {'z': '12'}}