Note Code added to the question demostrates why autovivification doesn’t happen. Short Your sub takes a list (hash) which has an anonymous array as an element – and %$headers is buried in that array. It is the anon array that is the scalar aliased to, thus there is no requirement for %$headers to … Read more
The easiest way is to construct your Hash with a block argument: hash = Hash.new { |h, k| h[k] = { } } hash[‘a’][‘b’] = 1 hash[‘a’][‘c’] = 1 hash[‘b’][‘c’] = 1 puts hash.inspect # “{“a”=>{“b”=>1, “c”=>1}, “b”=>{“c”=>1}}” This form for new creates a new empty Hash as the default value. You don’t want this: … Read more
If the amount of nesting you need is fixed, collections.defaultdict is wonderful. e.g. nesting two deep: myhash = collections.defaultdict(dict) myhash[1][2] = 3 myhash[1][3] = 13 myhash[2][4] = 9 If you want to go another level of nesting, you’ll need to do something like: myhash = collections.defaultdict(lambda : collections.defaultdict(dict)) myhash[1][2][3] = 4 myhash[1][3][3] = 5 myhash[1][2][‘test’] … Read more
What is the best way to implement nested dictionaries in Python? This is a bad idea, don’t do it. Instead, use a regular dictionary and use dict.setdefault where apropos, so when keys are missing under normal usage you get the expected KeyError. If you insist on getting this behavior, here’s how to shoot yourself in … Read more