Updating nested dictionaries when data has existing key

Question

I am trying to update values in a nested dictionary, without over-writting previous entries when the key already exists. For example, I have a dictionary:

Answer 1

This is a very nice general solution to dealing with nested dicts:

import collections
def makehash():
    return collections.defaultdict(makehash)

That allows nested keys to be set at any level:

myDict = makehash()
myDict["myKey"]["nestedDictKey1"] = aValue
myDict["myKey"]["nestedDictKey2"] = anotherValue
myDict["myKey"]["nestedDictKey3"]["furtherNestedDictKey"] = aThirdValue

For a single level of nesting, defaultdict can be used directly:

from collections import defaultdict
myDict = defaultdict(dict)
myDict["myKey"]["nestedDictKey1"] = aValue
myDict["myKey"]["nestedDictKey2"] = anotherValue

And here's a way using only dict:

try:
  myDict["myKey"]["nestedDictKey2"] = anotherValue
except KeyError:
  myDict["myKey"] = {"nestedDictKey2": anotherValue}