Adding Dictionaries Recursively In Python

I have the following two functions which take two dictionaries and recursively add their values. def recursive_dict_sum_helper(v1, d2, k): try: v2 = d2[k] except KeyError:

Solution 1:

If I understand right what you want to do, all of it could be achieved with the following code:

def dict_sum(d1, d2):
    if d1 is None: return d2
    if d2 is None: return d1
    if isinstance(d1, list) and isinstance(d2, list):
        return list(set(d1 + d2))
    try:
        return d1 + d2
    except TypeError:
        # assume d1 and d2 are dictionaries
        keys = set(d1.iterkeys()) | set(d2.iterkeys())
        return dict((key, dict_sum(d1.get(key), d2.get(key))) for key in keys)

dict_sum(a, b) will give the desired result.

Just note that it will raise an AttributeError if called with incompatible types such as

dict_sum({'a': 1}, 2)

Edit to treat lists specially (create list with unique elements).

Solution 2:

Made in one monster-generator as you seem to like it :)

def recursive_dict_sum(d1, d2):
    return dict((k, ((d1[k] if k in d1 else d2[k])
                       if k not in d1 or k not in d2
                      else (d1[k] + d2[k] if not isinstance(d1[k], dict)
                                        else recursive_dict_sum(d1[k], d2[k]))))
                for k in set(d1.keys() + d2.keys()))