How do we convert double nested dictionary to a list in Python?

Question

I want to convert

dct = {"a":1,"b":{"c":2,"d":{"z":5,"t":12}}} 

to

lst = ["a:1","b:c:2","b:d:z:5","b:d:t:12"] 

in Python?

Answer 1

Recursively:

def flatten(dct, path="",lst=None):
    if not lst: lst = []
    for key,value in dct.items():
        if type(value) is dict:
            flatten(value, f"{path}{key}:", lst)
        else:
            lst.append(f"{path}{key}:{value}")
    return lst

print(flatten({"a":1,"b":{"c":2,"d":{"z":5,"t":12}}}))

Outputs:

['a:1', 'b:c:2', 'b:d:z:5', 'b:d:t:12']

Another version, as suggested in the comments.
Credit to: @Ch3steR

def flatten(dct, path=""):
    lst = []
    for key,value in dct.items():
        if isinstance(value, dict):
            lst.extend(flatten(value, f"{path}{key}:"))
        else:
            lst.append(f"{path}{key}:{value}")
    return lst
 
print(flatten({"a":1,"b":{"c":2,"d":{"z":5,"t":12}}}))