shorthand way to create dictionary key if it does not exist

Question

I have a dictionary of zoo animals. I want to put it into the dictionary in a nested dictionary but get a KeyError because that particular species has not been added to the dictionary.

def add_to_world(self, species, name, zone = 'retreat'):
    self.object_attr[species][name] = {'zone' : zone}

Is there a shortcut to checking if that species is in the dictionary and create it if it is not or do i have to do it the long way and manually check if that species has been added?

Answer 1

def add_to_world(self, species, name, zone = 'retreat'):
    self.object_attr.setdefault(species, {})[name] = {'zone' : zone}

Answer 2

Here's an example of using defaultdict with a dictionary as a value.

>>> from collections import defaultdict
>>> d = defaultdict(dict)
>>> d["species"]["name"] = {"zone": "1"}
>>> d
defaultdict(<type 'dict'>, {'species': {'name': {'zone': '1'}}})
>>>

If you want further nesting you'll need to make a function to return defaultdict(dict).

def nested_defaultdict():
    return defaultdict(dict)

# Then you can use a dictionary nested to 3 levels
d2 = defaultdict(nested_defaultdict)
d2["species"]["name"]["zone"] = 1