from functools import reduce
d = {'0': {'key_x': 0, 'key_y': 15, 'key_z': 41}, '1': {'key_x': 5, 'key_y':
    22}, '2': {'key_x': 6, 'key_y': 41}}
reduce(set.intersection, map(set, list(d.values())))
Filter common sub-dictionary keys in a dictionary