def recursive_update(d, u):
    """
    Given two dictionaries d and u, update dict d recursively.

    E.g.:
    d = {'a': {'b' : 1}}
    u = {'c': 2, 'a': {'d': 3}}
    => {'a': {'b': 1, 'd': 3}, 'c': 2}
    """
    for k, v in u.items():
        if isinstance(v, collections.abc.Mapping):
            r = recursive_update(d.get(k, {}), v)
            d[k] = r
        else:
            d[k] = u[k]
    return d

    Given two dictionaries d and u, update dict d recursively.

    E.g.:
    d = {'a': {'b' : 1}}
    u = {'c': 2, 'a': {'d': 3}}
    => {'a': {'b': 1, 'd': 3}, 'c': 2}
    
sacred/utils.py