python - O(1) lookup of single tuple element in a dict? -

i have structure in mind similar dict tuples keys, except can entries 1 of tuple elements.

e.g. (something similar this. not real python code, idea)

>>> d[(100, "apple")] = 5.0 # putting entry dict >>> d[(100, "pear")] = 10.0 # putting entry dict >>> d[(200, "pear")] = 10.0 # putting entry dict >>> d[100] # o(1) lookup [("apple", 5.0), ("pear", 10.0)] >>> d["pear"] # o(1) lookup [(100, 10.0), (200, 10.0)] 

you can't defaultdict(). best way in python, or best data structure use? i'd lookup o(1), dict.

in case, neither tuple element unique, nor values.

i considering:

• nested dicts
• two dicts?
• some database-like structure

consider like:

class mydict(object):      def __init__(self):         self._data = {}      def __setitem__(self, key, val):         self._data[key] = val         if key[0] not in self._data:             self._data[key[0]] = {}         self._data[key[0]][key[1]] = val      def __getitem__(self, key):         return self._data[key] 

this allows lookup tuple or first element, both in o(1). can implement same key[1]. using dictionary of dictionaries makes subsequent lookup of other part of key o(1) too. in use:

>>> d = mydict() >>> d[100, "apple"] = 5.0 >>> d[100, "pear"] = 10.0 >>> print d[100] {'pear': 10.0, 'apple': 5.0} >>> print d._data {(100, 'apple'): 5.0, (100, 'pear'): 10.0, 100: {'pear': 10.0, 'apple': 5.0}} 

note assumes each combination key[0], key[1] have single val.

see e.g. how "perfectly" override dict? on making custom dictionaries.