Question

Working with deeply nested python dicts, I would like to be able to assign values in such a data structure like this:

  mydict[key][subkey][subkey2]="value"

without having to check that mydict[key] etc. are actually set to be a dict, e.g. using

  if not key in mydict: mydict[key]={}

The creation of subdictionaries should happen on the fly. What is the most elegant way to allow something equivalent – maybe using decorators on the standard <type 'dict'>?

Answer 1

class D(dict):
    def __missing__(self, key):
        self[key] = D()
        return self[key]

d = D()
d['a']['b']['c'] = 3