def recursive_items(dictionary):
for key, value in dictionary.items():
if type(value) is dict:
yield from recursive_items(value)
else:
yield (key, value)
a = {'a': {1: {1: 2, 3: 4}, 2: {5: 6}}}
for key, value in recursive_items(a):
print(key, value)
example_dict.get('key1', {}).get('key2')