A Dict class that can merge keys by applying function to the values associated with the keys to merge.

merge_dict.py

class MergeDict(dict):
    def __init__(self, *args, **kwargs):
        super(MergeDict, self).__init__(*args, **kwargs)
        self.key_parent = {}
        self.key_val = {}
    
    def find_rep(self, k):
        orig_k = k
        if k in self.key_parent:
            while k != self.key_parent[k]:
                k = self.key_parent[k]
        self.key_parent[orig_k] = k
        return k
    
    def merge_keys(self, k, l, merge_func=lambda k, l: k):
        k = self.find_rep(k)
        l = self.find_rep(l)
        self.key_parent[l] = k
        self[k] = merge_func(self[k], self[l])
        del self[l]
        return k
    
    def norm_val(self, k):
        return self[self.find_rep(k)]
    
md = MergeDict(a=1, b=2, c=3, d=4, e=5)
md.merge_keys('a', 'b', lambda acc, v: acc + v)
assert md.norm_val('b') == 3
assert md.norm_val('a') == 3
assert 'a' in md
assert 'b' not in md