Updating nested dictionaries when data has existing key

You can use collections.defaultdict for this, and just set the key-value pairs within the nested dictionary.

from collections import defaultdict
my_dict = defaultdict(dict)
my_dict['myKey']['nestedDictKey1'] = a_value
my_dict['myKey']['nestedDictKey2'] = another_value

Alternatively, you can also write those last 2 lines as

my_dict['myKey'].update({"nestedDictKey1" : a_value })
my_dict['myKey'].update({"nestedDictKey2" : another_value })

You can write a generator to update key in nested dictionary, like this.

def update_key(key, value, dictionary):
        for k, v in dictionary.items():
            if k == key:
            elif isinstance(v, dict):
                for result in update_key(key, value, v):
                    yield result
            elif isinstance(v, list):
                for d in v:
                    if isinstance(d, dict):
                        for result in update_key(key, value, d):
                            yield result

list(update_key('Any level key', 'Any value', DICTIONARY))

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:

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