Python version of Clojure's merge-with and deep-merge-with

deep_merge_with.py

import operator
import itertools

def merge_key_with(f, k, dicts) :
    if all((k in d) for d in dicts) :
        return f(*(d[k] for d in dicts))
    else :
        first = next(itertools.ifilter(lambda d : k in d, dicts))
        return first[k]

def merge_with(f, *dicts) :
    all_keys = set(itertools.chain(*(d.iterkeys() for d in dicts)))
    return dict((k, merge_key_with(f, k, dicts)) for k in all_keys)

def deep_merge_with(f, *dicts) :
    def merge(*items) :
        if all((type(d) is dict) for d in items) :
            return merge_with(merge, *items)
        else :
            return f(*items)
    return merge(*dicts)


u = {"a": {"b": {"c":1, "d":{"x":1, "y":2}}, "e":3}, "f":4}
v = {"a": {"b": {"c":2, "d":{"z":9}, "z":3}, "e":100}}

print u
print v
print deep_merge_with(operator.add, u, v)