Merging two dictionaries

[Peter Otten]

Douglas Garstang wrote:

> I have the two dictionaries below. How can I merge them, such that:
> 
> 1. The cluster dictionary contains the additional elements from the
> default dictionary.
> 2. Nothing is removed from the cluster dictionary.

def inplace_merge(default, cluster):
    assert isinstance(default, dict)
    assert isinstance(cluster, dict)

    d = set(default)
    c = set(cluster)
    default_only = d - c
    both = d & c
    for key in both:
        dv = default[key]
        cv = cluster[key]
        if isinstance(cv, dict):
            inplace_merge(dv, cv)
    cluster.update((dk, default[dk]) for dk in default_only)

should work once you've fixed your example dicts.

Peter