flip keys and values in dictionary python

Question

I have a dictionary called z that looks like this

---

{0: [0.28209479177387814, 0.19947114020071635, 0.10377687435514868, 0.07338133158686996], -1: [0.282094791773878

Answer 1

As you have already seen in the comments on your question, Python dictionaries cannot have duplicate keys, since there would be uncertainty as to a correct single value given a key

This could be fixed by having parallel structure to the first, so instead of {value:key}, it would be {value:[key1, key2]}. The code to generate it would be:

new = {}
for key, value in z.items():
  if not value in new:
    new[value] = []
  new[value].append(key)

See Adam Smith's answer for more details.