How to combine two dictionaries? One dict as key, another dict as value

Question

I have two dictionaries

Dict0 = {'a':0, 'b':1, 'c':2}

Dict1 = {0 : {'a0' : 0,'a1' : 1,'a2' : 2},
         1 : {'b0' : 0,'b1' : 1,'b2' : 2},
         2 : {'c0' : 0,'c1' : 1,'c2' : 2}}

I would like to get a combine dictionary CombDict , which uses keys of Dict0 as the values for CombDict , and uses values of Dict1 as the keys for CombDict

CombDict = {{'a0':0,'a1':1,'a2':2}:'a',{'b0':0,'b1':1,'b2':2}'b',{'c0':0,'c1':1,'c2':2}:'c'}

I know it's very basic. My logical code is written, but definitely is wrong.

CombDict = {}
for k0, v0 in Dict0:
    CombDict.values()= k0
    for k1,v1  in Dict1:
        CombDict.keys() = v1

Any suggestion? Thanks. Btw if you want to make the dictionaries more sense to you, just edit them.

Answer 1

Because dictionaries are mutable, you cannot use dictionaries as keys of another dictionary or store them in a set.

You'll have to capture an immutable 'snapshot' of the dictionary instead:

def dict_to_key(d):
    return tuple(sorted(d.items()))

Provided the dictionary values are not mutable either, you can use the return value of the dict_to_key() function as keys instead.

Now you can build the combined dictionary:

CombinedDict = {dict_to_key(Dict1[v]): k for k, v in Dict0.items()}

Demo:

>>> Dict0 = {'a':0, 'b':1, 'c':2}
>>> Dict1 = {0 : {'a0' : 0,'a1' : 1,'a2' : 2},
...          1 : {'b0' : 0,'b1' : 1,'b2' : 2},
...          2 : {'c0' : 0,'c1' : 1,'c2' : 2}}
>>> def dict_to_key(d):
...     return tuple(sorted(d.items()))
... 
>>> {dict_to_key(Dict1[v]): k for k, v in Dict0.items()}
{(('b0', 0), ('b1', 1), ('b2', 2)): 'b', (('a0', 0), ('a1', 1), ('a2', 2)): 'a', (('c0', 0), ('c1', 1), ('c2', 2)): 'c'}