dictionary - Python-how to merge and not update two dictionaries with strings as keys and values as list of strings? -

given 2 dictionaries:

d1={'cardinal':['va','oh'], 'meadowlark':['or']} d2={'meadowlark':['wy'], 'cardinal':['va', 'il'], 'oriole':['md']} 

how merge them new dictionary without updating original dictionaries and concatenate duplicates so:

new_dict={'cardinal':['va','oh','va','il'],'meadowlark':['or', 'wy'], 'oriole':['md']} 

my code doesn't concatenate correctly here is:

def merge(d1,d2):     import collections     a=collections.counter(d1)     b=collections.counter(d2)     return a+b 

i'm stuck on how concatenate items.

deep-copy 1 of dicts, extend values elements of values other dict needed.

>>> copy import deepcopy >>> d1={'cardinal':['va','oh'], 'meadowlark':['or']} >>> d2={'meadowlark':['wy'], 'cardinal':['va', 'il'], 'oriole':['md']} >>>  >>> d = deepcopy(d1) >>> key, lst in d2.items(): ...     d.setdefault(key, []).extend(lst) ...  >>> d {'meadowlark': ['or', 'wy'], 'oriole': ['md'], 'cardinal': ['va', 'oh', 'va', 'il']} >>> d1 {'meadowlark': ['or'], 'cardinal': ['va', 'oh']} >>> d2 {'meadowlark': ['wy'], 'oriole': ['md'], 'cardinal': ['va', 'il']}