Ultimatt

    my $a = ["foo", 123, {"bar" => [[1,2,3], {"qux" => "quux"}]}];
    $a->[2]{"bar"}[1]{"spam"} = "eggs";
    use JSON;
    print(encode_json($a))

    use JSON;
    my $a = [];
    $a->[2]{"bar"}[1]{"spam"} = "eggs";
    print(encode_json($a))

    import json
    from collections import defaultdict

    # recursive defaultdict using lambda
    datastructure = lambda: defaultdict(datastructure)

    a = [None] * 3
    a[2] = datastructure()
    a[2]["bar"][1]["spam"] = "eggs"

    print(json.dumps(a))

    import json
    from collections import defaultdict

    def datastructure():
       return defaultdict(datastructure)

    a = []
    # expand list to at least length 3
    while len(a) < 3:
       a.append(None)
 
    a[2] = datastructure()
    a[2]["bar"][1]["spam"] = "eggs"

    print(json.dumps(a))