How can I detect "missing" keys from a Python dict?

Question

I have the following Python dict:

d = {'A-x': 1, 'A-y': 2,
     'B-x': 3,
     'C-x': 4, 'C-y': 5,
     'D-x': 6, 'D-y': 7,
     'E-x': 8}

Where the keys here represent a "Level-SubLevel" pattern.
There is no B-y or E-y key and they can therefor be considered "missing".

I'm trying to detect these "missing" key Levels, so my expected output would be the list:

['B', 'E']

So far I have the following working solution...

import numpy as np
from itertools import product

a = np.array([k.split('-') for k in d])
all_keys = ['-'.join(x) for x in list(product(set(a[:, 0]), set(a[:, 1])))]
missing_keys = [x.split('-')[0] for x in all_keys - d.keys()]

... but I feel there must be a better/cleaner solution - ideally using the standard python library.

I should clarify also, that in this particular case, the "SubLevel" portion of the key can only be 1 of 2 possible values. So only "x" or "y". Also "...-x" will always exist, it's only possible that "...-y" may be missing.

Any suggestions would be much appreciated.

Answer 1

After clarifying in your question, that only '-y' keys might be missing, you can try this:

d = {'A-x': 1, 'A-y': 2,
     'B-x': 3,
     'C-x': 4, 'C-y': 5,
     'D-x': 6, 'D-y': 7,
     'E-x': 8}

out = [k for k in set(k.split('-')[0] for k in d) if not k+'-y' in d]
print(out)

Prints:

['B', 'E']